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COUNTRY LIFE EDUCATION 
SERIES 

Edited by 

Charles William Burkett 

Kansas State Agricultural College 

Types and Breeds of Farm Animals 

By Charles S. Plumb, Ohio State University 

Principles of Breeding 

By Eugene Davenport, University of Illinois 

Other vohtines in preparation 



PRINCIPLES OF BREEDING 



A TREATISE ON THREMMATOLOGY 

OR 

THE PRINCIPLES AND PRACTICES INVOLVED IN THE 
ECONOMIC IMPROVEMENT OF DOMESTI- 
CATED ANIMALS AND PLANTS 



BY 



E. DAVENPORT, M.Agr., LL.D. 

Professor of Thremmatology in the University of Illinois 

Dean of the College of Agricultiire 

Director of the Agricultural Experiment Station 



WITH APPENDIX 

BY 

H. L. RIETZ, Ph.D. 

Assistant Professor of Mathematics in the University of Illinois 



GINN & COMPANY 

BOSTON . NEW YORK • CHICAGO • LONDON 



[UBHARY of CONGRESS j 
Two CoDles Received 

OCT 4 »907 

, Copyncttt Entry 

io^s A XXc, n/ 



eopY 



c.-'^ 

^ 






^ 



o1 



Entered at Stationers' Hall 



Copyright, 1QO7 
^ By EUGENE DAVENPORT 



all rights reserved 



y^ 



1-V^^^^ 



aCfyt atfjenxum j^retfcf 



GINN & COMPANY • PRO- 
PRIETORS ■ BOSTON • U.S.A. 



PREFACE 

Two classes of people have been in mind in the preparation of 
this text, viz. the student of agriculture in the college and experi- 
ment station and the practical breeder upon the farm . Both need 
to know all that evolution has to teach of methods that may be 
employed in still further adapting to our needs such animals and 
plants as hav^e been domesticated because of their valuable natural 
qualities. 

The general purpose has been first of all to define the problems 
involved in animal and plant improvement ; to free the subject 
from the prejudice and tradition that have always befogged it ; 
to bring to the study whatever facts are fully l^nown to biological 
science ; to recognize and define somewhat clearly the present 
limitations of knowledge, and to indicate as Veil as may be the 
directions from which further and much-needed light is most 
likely to come. Last of all and more than all, it has been the »«5^ ^" 
purpose to encourage, and if possible induce, more exact methods 
of study and of practice than have hitherto characterized this 
branch of agricultural science. 

It is yet too early to prepare an ideal treatise upon this most 
intricate subject, and no one is more conscious than the author 
of the many deficiencies and shortcomings of this attempt. Some 
effort, however, is surely needed at this time to clear the atmos- 
phere, to give the student of agriculture at least a rational point 
of view, and to bring him into comradeship with those who are 
earnestly studying biological problems and through whose efforts 
these vexed questions are sure sooner or later to find a solution. 
This, together with the pressing need of a text in his own class 
room, is the author's only warrant for the present volume. 

No new theories of evolution are proposed. The chief object 
has been to distinguish what is known from what is merely tradi- 
tional ; to give as much as possible, within the limits of available 
space, of the best established facts bearing upon this subject ; to 



vi PREFACE 

call attention to approved methods of study, and to indicate lines 
of research most likely to furnish valuable information in the not 
distant future. 

It is necessary to introduce a considerable amount of mathe- 
matical work in the later chapters. No excuse is offered for this 
introduction, and it is earnestly desired that the reader give 
special attention to this portion of the text, whether easy or diffi- 
cult of following, because it is by this road that many new princi- 
ples will arrive and that many of our future operations must be 
ordered ; for nothing is clearer than that the successful breeder 
of the future ivill be a bookkeeper and a statistician. For the 
convenience of the non-mathematical reader general formulae are 
placed in footnotes, and some of the more abstract matter is 
placed in the form of an appendix for the benefit of the more 
mathematically inclined. 

The writer has taught this subject for fifteen years and is fully 
aware of the pedagogic difficulties involved as well as of the 
limitations of knowledge. He has tried many different outlines 
and many different methods of presentation, and has chosen the 
one here employed because in experience it seems the most 
favorable for the presentation of the subject-matter involved and 
at the same time for putting the student in a frame of mind 
favorable for the undertaking of economic breeding operations 
and for the reception of new truths as they shall be discovered. 

Variation rather than heredity has been chosen for the initial 
and leading thought because better calculated, as experience has 
shown, to afford a favorable outlook and to develop such con- 
ceptions of evolution as are most useful later on. 

The evolutionist who might chance to scan these pages would 
be struck by the absence of some of the cardinal features of 
evolution, as he would also note the exceeding prominence given 
to certain other questions of seeming minor importance. Herein 
exists the difference between thremmatology and evolution, and 
this very matter has given the author more difficulty than all 
others, viz. to rearrange values and to determine proper relations 
of old questions in a new field. 

We must discuss the causes of variation even though we are 
told by the best students that such attempts are premature. A 



PREFACE vii 

minor matter in evolution, curious rather than otherwise, it is a 
vital one in thremmatology, and we must discuss the subject the 
best we are able, if only to learn how little we really know about 
it and to point attention in the right direction. 

No attempt has been made to include exhaustive references. 
On the other hand, they are confined for the most part to a few 
standard books easy of access, and to save time the references 
are mostly to definite pages. A general and more extended list 
follows the summary of nearly every chapter, enabling the student 
to pursue that particular subject further if desired ; but there is 
no attempt at a complete bibliography. It was hoped that if the 
list of references could be kept small the student and the breeder 
would be the more likely to provide themselves with standard 
literature bearing on the subject. I have made the freest use of 
standard authors, giving full credit in all cases, generally in the 
form of reference to text and page. This course has been dictated 
by the desire to furnish the student with reliable facts rather 
than a series of academic discussions upon disputed subjects. 

I desire to acknowledge the very great services of Dr. Rietz, 
to whom I am indebted for much assistance in the more statistical 
portions, and for the preparation of the appendix especially 
directed to the mathematical student, not as a text but as an 
introduction to further study in this special phase of science. 

I am also indebted to many of my colaborers in the Univer- 
sity of Illinois and elsewhere, as well as to numerous breeders in 
this and other states, who by their assistance have contributed 
much to any success which this volume may meet. 

Its possible merits, therefore, I must share with others ; its 
defects and shortcomings are my own. 

E. DAVENPORT 

University of Illinois 
Urbana 



CONTENTS 



INTRODUCTION 



Page 



PART I — VARIATION 



I. Variation in General .... 

I. Variation Universal among Living Beings 

II. Variability the Basis for Improvement 

III. Nature of Variability .... 

IV. Meaning of the Term "Character" 
V. Dominant and Latent Characters 

VI. The Unit of Variability 
VII. Distinctions as to Kinds of Variations 
References . 

II. MORPHOH)GICAL VARIATION 

References . 

III. Substantive Variation 

IV. Meristic Variation 

I. Symmetry . 

II. Meristic Variation in Linear Series 

III. Meristic Variation and Bilateral Symmetry 

IV. Symmetry in Variable Parts 
V. Meristic Variation in Radial Series 

VI. Importance of Meristic Variation 

References ...... 

V. Functional Variation .... 

I. Variation in the Degree of Activity of Normal Functions be- 
tween Different Individuals of the Same Species . 
II. Variation in the Degree of Activity of Normal Functions within 
the Same Individual ........ 

III. Modification of Normal Functions by External or Other Influ- 

ences ........... 

IV. Normal Functions exercised under Abnormal Conditions . 

References .......... 



13 
IS 

17 
24 

25 
29 

30 

33 

34 
39 
65 
68 

70 
73 
74 

75 

77 
9' 



107 
1C9 



VI. Mutations no 

I. Distinction between Mutation and Ordinary Variation . .110 

II. Examples of Mutation . . in 

ix 



CONTENTS 



Chapter 



III. Experiments of De Vries . 

IV. American Experiences 

V. Economic Significance of Mutations 
VI. Biological Significance of Mutations 
References . . . . . 




PART II — CAUSES OF VARIATION 



VII. 



iNTROnUCTION 

The Mechanism of Development and Differentiation 

I. Protoplasm the Physical Basis of Life . . . . 
II. The Cell the Unit of Structure . . . . . 

III. Mechanism of Cell Division (Mitosis) . . . . 

IV. Cell Division with and without Differentiation 
V. Physiological Units 

References ......... 



VIII. Internal Causes of Variation 



/. INTERNAL INFLUENCES AFFECTING PRIMARILY THE IN- 
DIVIDUAL 

I. Cell Division ......... 

II. Bisexual Reproduction a Fundamental Cause of Variation 

III. Maturation and the Reduction of the Chromosomes a Cause 

of Variation ........ 

IV. Bud Variation ......... 

V. Influence of the Condition of the Germ upon Development 

VI. Xenia, or Fertilization of the Endosperm 
VII. Telegony .......... 

VIII. Intrauterine Influences ....... 

IX. Reversion and Atavism ....... 

X. Individual Characters dependent upon Sex 
//. INTERNAL INFLUENCES AFFECTING THE RACE AS A 

WHOLE 

XI. Relative Fertility, or Genetic Selection .... 
XII. Physiological Selection ....... 

XIII. Selective Death Rate ; Longevity ..... 

XIV. Bathmic Influences ........ 

XV. Physiological Units ........ 

XVI. Germinal Selection ........ 

References ......... 

IX. External Influences as Causes of Variation 

I. General Effect of Locality upon Plant and Animal Develop 
ment ......... 

II. Influence of Food upon Variability 

III. Effect of Moisture upon Development 

IV. Effect of Contact upon Protoplasmic Activity . 
V. Effect of Gravity upon Living Matter ; Geotropism 

VI. Effect of Light upon Living Matter 



CONTENTS 



XI 



Chapter 

VII. Influence of Temperature upon Living Matter 
VIII. Effect of Chemical Agents upon Protoplasmic Activity 

IX. Effect of Saline Solution upon Development in Aquatic 
Animals ........ 

X. Influence of Use and Disuse upon Development 
XL External Influences as Causes of Variation in Type 
References ......... 

X. Relative Stability and Instability of Living Matter 
I. Evidence from .Stability of Type .... 

II. Evidence from Mutability of Species 
III. Evidence from Reversion and Atavism 
IV. Evidence from Disappearance of Parts 

V. Evidence from the Direct Action of the Environment 
VI. Evidence from Acclimatization .... 

VII. Evidence from Regeneration ..... 

VIII. Internal Factors in Regeneration .... 

IX. Evidence from Grafting ...... 

X. Evidence from the Origin of New Cells and Tissues 
XL Evidence from Development and Differentiation 

References ........ 



254 
264 

282 

285 
290 
294 

295 
296 
298 

305 
306 

307 
308 
316 
332 
335 
336 
338 
345 



XI 



XII. 



PART III — TRANSMISSION 

Transmission of Modifications due to External Influences 

I. Introductory ..... 

II. Evidence from the Nature of Variation 

III. Evidence from Mutilations 

IV. Evidence from Food Supply 

V. Evidence from Acclimatization . 

VI. Evidence from Habit and Instinct 

VII. Evidence from Use and Disuse 

VIII. Evidence from Disappearing Organs 

IX. Variations due to Causes not affecting the Germ are not 

Transmitted .... 

References .... 



Type and Variability 

I. Type ........... 

II. Variability, or Deviation from Type ..... 

III. Practical Hints on the Taking and Grouping of Measurement 

IV. Probable Error ......... 

V. Comparative Type and Variability for Different Characters in 
the Same Population ....... 

VI. Effect of Selection upon Type and Variability 
VII. Indirect Effects of Selection upon Type and Variability . 
VIII. Studies in Type and Variability of the Same Variety of Co 
raised under Different Conditions as to Fertility . 
References 



348 
348 
356 
364 
370 
374 
386 
404 
409 

416 
418 

419 

420 
425 
435 
437 

444 
445 
447 

449 
452 



Xll 



CONTENTS 



Chapter 

XIII. CORRKLATION 



Pace 



XIV. 



I. Meaning of Correlation 
II. Calculation of Coetiftcients of Correlation 
III. The Correlation Table .... 
IV. The Correlation Coefficient . 
V. The Regression Coefficient . 
VI. Studies in Speed Records of Trotters . 
References ...... 



Heredity 

I. How Characters behave in Transmission 
II. Statistical Methods of Study of Heredity 

III. The Regression Table .... 

IV. Like Parents beget Unlike Offspring and, conversely, Like 

Offspring may be begotten by Unlike Parents . 
V. Regression. In general, the Offspring is More Mediocre 
than the Parents ; that is, Whatever the Parentage, the 
Offspring exhibits a Strong Tendency to regress toward the 
Mean of the Race .... 

VI. The Measure of Heredity 

VII. The Mean of the Offspring not necessarily the Same as the 

Mean of the Parentage 

VIH. Extremes of a Race relatively Less Productive than the 

Means ...... 

IX. Progression. Parents in general produce a Few Individuals 

More Extreme than the Race 

X. The Exceptional Individual arises either from Mediocrity 

or from the Exceptional Parent 
XL Fraternal Variability, — Offspring of Same Parents nol 
Identical ... ..... 

XII. Characters tend to combine in Definite Mathematica 
Proportions ........ 

XIII. Mendel's Law of Hybrids 

XIV. The Law of Ancestral Heredity ..... 
XV. Limit to the Reduction of Variability .... 

XVI. Power of Selection to permanently modify Types by the 

Establishment of Breeds 

XVII. Breeding True, or Stability of a Character established by 

Selection ........ 

XVIII. Duration of Varieties, Breeds, and Family Strains 
References ........ 



XV. Prepotency 



I. Data from the Trotting Records illustrating Prepotency 
II. Prepotency in Sex ........ 

III. Influence of Age on Prepotency ..... 

IV. Influence of Constitutional Vigor upon Prepotency 
References ......... 



CONTENTS 



Xlll 



PART IV— PRACTICAL PROBLEMS 



Chapter 
XVI. 



Selection .... 

I. Ideals in Selection 
II. Historical Knowledge of the 

III. General Principles involved i 

IV. Rational Selection 



Breed Necessary 
n Selection 



XVII. Systems of Breeding . 

I. Purposes in Breeding . 
II. Grading .... 

III. Crossing or Hybridizing 

IV. Line Breeding 
V. Inbreeding 

VI. Breeding from the Best 
References 

XVIII. The Determination of Sex 

I. Theories 
II. Influence of Nutrition . 

III. Influence of Fertilization 

IV. Sex in Mammals . 
V. The Accessory Chromosome 

References 

XIX. Plant Breeding . 

I. Advantages and Limitations 
11. Soil and Culture Conditions 
III. Systems of Planting 
References 

XX. Animal Breeding 

I. Advantages and Disadvantages 
II. Fewer Characters for Selection 

III. Fashion ..... 

IV. Show-Ring Consequences 

V. Testing of Sires and Dams . 
VI. Weathering a Period of Depressio 

VII. Records 

VIII. Disposal of Surplus Females 
IX. A Market for Sires 

X. Community Breeding 
XL The Young Breeder 

References .... 

XXL Development .... 

APPENDIX 

INDEX 



Sex Determinat 



the 



Herd 



577 
578 
579 
581 
592 

599 

599 
602 
6c8 
610 
613 
626 
628 

629 

629 

631 
632 

634 
634 
637 

639 

639 
641 

643 
651 

654 

654 
656 
658 
660 
660 
665 
666 
672 

673 
674 

675 
676 

677 
681 



THE PRINCIPLES OF BREEDING 

THREMMATOLOGY 

INTRODUCTION 

The main title of the present volume was chosen because self- 
explanatory, though it less accurately expresses the scope of the 
subject than does the sub-title, which is only beginning to come 
into general use. 

Thremmatology, from the Greek tJircninia, a thing bred, is a 
term proposed by Ray Lancaster ^ to cover the principles and 
practices concerned in the improvement of domesticated animals 
and plants. 

The term is broader than the " principles of breeding " because 
it includes development as well as reproduction. It is distinct 
from evolution in general, which attempts to explain the princi- 
ples and forces connected with the origin and development of all 
forms of life but without the slightest reference to economic 
considerations. In evolution a protozoon is as important as a 
pig, a hydra of as much significance as a horse, and the njost 
pestiferous weed as much an object of interest as either corn 
or wheat. 

Thremmatology limits itself to those species and varieties whose 
natural qualities made them useful to man in the beginning, and 
it asks and seeks to answer this one question. How can they be 
made still more useful and better adapted to the purposes of an 
advancing civilization } In this study forms of life that are of no 
economic value are of no special concern except as their consider- 
ation may throw light upon domesticated forms. This latter is 
often the case, for it is doubtless true that the same principles 
apply to all species, economic or otherwise, because none were 

^ See Encyclopedia Britannica, ninth edition, XXIV, 841. 



2 INTRODUCriON 

si)ccially created lor man any more than lOr any other animal. 
It is a general biol<)L;ical truth that everythini;" lives unto itself, 
— not where it choses but where it can ; not upon what it likes 
best but ui)on what it can get. 

It may seem to the student that an undue amount of attention 
is given to variation and that a disjjroportionate amount of space is 
devoted to that subject. In that event I have to say that variation 
is not the antithesis of heredity but rather its constant and insep- 
arable attendant, and that the facts of variation constitute the 
best portion of that stock of information with which the student 
must become possessed before he is ready to study the principles 
involved in those generalizations ui)on which i)ractical operations 
may be safely based. 

One is painfully aware, too, of the necessity of ranging far and 
wide for facts, and the student cannot fail to feel ofttimes that 
the subject-matter in hand is far removed from agriculture. When 
this is the case it is because we arc forced to take what is avail- 
able and make the most of it. Unfortunately the workers in 
strictly agricultural fields are all too few and the reliable data 
deplorably meager, though some original and I trust valuable 
matter has been recently added to our stock of knowledge. 

While the same principles doubtless apply in thremmatology 
as in evolution, yet important distinctions are to be observed. 
First, there is every reason to suppose that even fundamental 
laws apply to different species in different ways. For examj^le, 
Indian corn seems particularly sensitive to close breeding, whereas 
wheat is almost exclusively inbred and has been so inbred for 
unknown generations. Again, the circumstances of the case 
often introduce into the problem certain economic considerations 
not resting upon general evolution. Iu)r examjile, man cannot 
afford the "countless ages " and "untold generations " which are 
accorded nature for accomplishing results. In practical breeding 
operations substantial results must follow at once and exhibit a 
high degree of success within the period of a lifetime or they will 
be discarded as valueless. 

Experience shows that the purposes, standards, and methods 
of a successful breeder are seldom handed down from one man 
to another, even to his own son. Even if that could be done, it 



INTRODUCTION 3 

would constitute no exception to the rule that a man must real- 
ize the fruit of his own labors and in his own generation, for 
breeding is a business and must be made to pay. The breeder 
must therefore work faster than nature, and thremmatology can- 
not make use of a leisurely operating evolutionary principle unless 
its action can be accelerated or its cumulative effects exaggerated. 
Yet again, man cannot afford the immense numbers and the whole- 
sale destruction that characterize nature's methods of working 
changes. Animals and even plants cost money, and a relatively 
large proportion must meet the conditions, or the enterprise must 
be abandoned. 

Business considerations therefore set arduous limitations upon 
thremmatology in respect to both time and numbers from which 
evolution in general is entirely free. The breeding business has 
its own particular problems, some of the most important of which 
unfortunately the known facts of evolution are least able to 
answer. The profitable study of this subject will, however, be 
assisted by a clear statement of these problems. 

The problems of the breeder. Certain questions stand clearly 
out in the minds of practical breeders, and though an attempt 
to answer them seriatim would not be the best method of study, 
and though some of them cannot be answered with certainty 
in the present state of knowledge, yet nothing is of more con- 
sequence at the outset than that the student get a clear idea of 
the problems needing solution and towards whose solution the 
study of thremmatology is directed. They are substantially as 
follows : 

To what extent are the characteristics of an individual at matur- 
ity due to its ancestry (heredit)), and to what extent are they 
due to the conditions of life (environment), such as food, climate, 
exercise, and general care during development ? 

Are the influences of the conditions of life limited to the indi- 
vidual or are they in certain instances and to some extent carried 
over upon the offspring ? that is, are the effects of envirfmment 
inherited ? 

Can variations be directly controlled to any extent whatever, 
or only indirectly through selection and by special care during 
development ? 



4 



IN I'KOnill'lON 



I low rltiHtiM" is scK'it ion in conl i ollmi; \.iii,ition? ill, it is. an." 
i-onj;cnit.il x.ni.itions ilur rnliri'K to pau-nta^c or an- llu-n" hack 
ol the i\uontai;r ivitain inhcivMil and (.-onstitutional Iciulcncios 
that lai\!L;x"l\' iix the i;cnoial iHiciiion ol \aiiations, indcpiMulcnt 
ol solortion ? 

DiH's iniproxonuMit consist in raisins; the slandard ahsoUitoly or 
onl)' in raisin^; the _i;vnoral a\oia,i;c h\- ohminatini;' tho loss dosir- 
ahlo ? that is. <loi>s hioodinj;' improve upon ihe host or doos it 
only hrinj; tho _i;iMUMal mass noaror to iho nppor lowl ? 

I'o wliat oxtont is oxolution a <;ra(hial pnnoss and to wliat 
o\tonl ma\' prolound aiKani'os appear siuldonh . as in sports ? 
and is the one class ol improx oniont an\ more poimanont or roli- 
ahlo than the othoi' ? 

1 )o all possihlo \ahios ol a \ariahlc oharaitcM' appear or arc 
certain values seKlom or nexer presented ? that is to say. is 
variation al\va\s eonlimious or is it sometimes diseontinuous, 
making' certain things impossihle hecause [\\c propiM' filia- 
tions or eomhinations i\i) not appear o\\ which selection may 
he hased ? 

\\ hat \ariatiiMis are most likeh to appear in successive gener- 
ations ol an\' _i;i\en hreed. \ariet\. or l\pe? 

.Are variations ci)rrelaleil ? that is, do they teml at ail to move 
together, sui^'-^estini;" lelations ol cause and effect ? 

What art." the jMoper standards h>i' selcctiiMi ? I low nuuh shall 
ho i;i\en \o utilit\- and hmv much to appearance? 

To what extent is individual excelleiu~i" a sale i;uide to breet.!- 
inj;" powers ? 

To what extent is the offspring;' like the inunediate parent and 
to what extent does it resemble more remote ancestors ? 

What is the relatixe inlhience of sire and dam with respect to 
transmission of chaiaclers ? 

To what extent k\o the condition iA the male at the lime of 
service and the care oi the female durini;' pre_i;nanc\- inlhience 
the olfsprins;" ? 

What aie the real dani;ers from (."lose breeding, it an\. and are 
the\- certain or only jirobable ? 

llow can the ad\anta.<;es of close or line breeding be realized 
without encounterinL! its danuers ? 



Ii\"l PC)!)! f I ir)N 



5 



Will a ^ivcn brccfl, variety, or family strain cnfliirc inrlcfi- 
nilcly iiriflcr pro|><;r cnifiitions or will it inevitably "run out," 
necessitating a constant return to founrJation stock for new 
cf>mbinations as the fjasis of improverl strains ? 

What arc the laws that determine the sex of offspring ? 

Do the same laws of breeding aj^jjly equally to animals and to 
plants anfl to all species and varieties alike, or rlo rlifferent species 
operate vmrler somewhat flifferent laws ? 

Is a given species, variety, or breed always subject to the same 
laws ? that is, are identical variations always due to the same 
causes and do given causes always jjrfxluce the same effects ? 

How can results be secured with the least wastage either in 
time or numbers ? 

Upon the answers to these questions will depenrl the policies 
of all breeding enter[jrises and the permanent value of particular 
family strains. Upon some of these points there exists much 
specific and reliable information ; upon others, unfortunately, the 
evidence is yet scanty and uncertain. At the present rate of 
progress, however, we will not have long to wait for much addi- 
tional knowledge. In the meantime we must make the best use 
f possible of the information and experience at hand. 

These problems can best be answered not by directing atten- 
tion tr> each separately, because they overlap, but rather by follow- 
ing out what are known to be the characteristic lines of study in 
the subject as a whole. The order pursued in this brK>k is the one 
believed to be most favorable both for this purpose and for the 
most successful answering of these definite questions.' 

' A fair knowledge of general evolution i.s presumed on the part of the student 
and reader. If this is not in his possession, he will do well to read at least 
J Irwin's <^Jrigin of Species for a broad though now somewhat old and incomplete 
outlook upon the general field. If he desires to go further and enter the field of 
controversy, he can do so most directly by readmg Weismann's Kssays on 
Heredity and his Germ I'lasm, together with Romanes' Examination of Weis- 
mannism and his two volumes of I>arwin and y\fter Darwin. If this is done, it 
would be well to fini.sh with Habit and Instinct by Morgan. 



Part I — Variation 
CHAPTER I 

VARIATION IN GENERAL 

SECTION I— VARIATION UNIVERSAL AMONG LIVING 

BEINGS 

The most obvious fact about living beings is their variability. 
Not only do species differ from each other by many and widely 
different characters, but individuals within the species are distin- 
guished by differences readily discernible, at least by the trained 
observer. The general differences between horses and cattle, for 
example, are specific and distinct and therefore striking even to 
the casual observer ; but to .the trained eye all horses are not 
alike, and so it is that differences are detected within the species. 
Two individuals may be recognized as possessing the same char- 
acters and therefore related by descent, but invariably these 
characters differ in degree or in their proportions one to another. 

Two animals may be of the same or of different colors, but in 
either event the parts are differently proportioned. The leg of 
one is longer, larger, or more crooked than that of the other. 
The bones composing the two are not of equal, or even of pro- 
portional, lengths. Two cows of the same breed differ marvel- 
ously in the amount of milk they can yield in a year, and some 
are known to produce three times as much butter fat as others 
from the same amount of the same kind of feed.^ Again, some 
milk is rich in fat (6 or even 8 per cent) while other is poor 
(2 per cent or even less). Some horses, because of their con- 
formation, travel more easily or more rapidly than others, and 
some are more intelligent or more enduring or more docile. 

1 See data from Agricultural Experiment Station, University of Illinois. 

7 



8 VARIATION 

Some dogs (bloodhounds) trail marvelously well ; others (grey- 
hounds) scarcely at all. Some hens lay more eggs than others, 
and of different color and size. 

Some animals are hard feeders, while others lay on flesh 
readily. Some beef is coarse in its grain ; other is fine and ten- 
der. Some is well marbled with fat ; other is not. Sometimes 
the flavor is dehcate ; again it is rank, and often it is insipid. 

No two trees are alike in their growth or branching habit, 
though similar within the same variety, and the widest difference 
is often found in leaves from the same tree. 

Differences extend to minute particulars and include all charac- 
ters. The student should early form a clear conception of the 
fact that differences extend to all characters however insignifi- 
cant or minute. Besides, he should understand that they include 
function as well as structure, and that not only external anatomy 
and conformation are involved but internal organs and their 
activity as well, and no greater mistake can be made than to 
define evolution as " a study in morphology." 

If we so define the word " variation " as to cover any change 
in detail of structure or function which our faculties enable us 
to detect, then we may say that variation extends to all charac- 
ters, internal or external, structural or functional, and if the 
study lay in the realm of ethics, economics, philosophy, or reli- 
gion, we should add, material or immaterial. 

The individual is therefore so distinctly a unit that its iden- 
tity is at once recognized and the principle is conceded that " no 
two are alike " and that variation is universal. 

Limitation of variability. The exception to the universality 
of variability is in the realm of non-living matter. The specific 
gravity and other properties of iron, gold, sodium, or chlorin 
are constant, and their relations and combining powers with 
other chemical substances are, under identical conditions, invari- 
able and therefore well known. 

Oxygen, hydrogen, and even nitrogen and carbon, combine 
always in definite proportions, and though their combinations 
are exceedingly numerous yet when the conditions are known 
the exact combination can be foretold ; moreover the properties 
of this combination will not only be definite but they will be 
identical with those of all other similar compounds. In this 



VARIATION IN GENERAL 9 

way sodium chlorid, for example, has always definite and well- 
known properties not subject to variability. 

It is to be noted of course that the properties of the com- 
pound NaCl are totally different from the properties of the ele- 
ments that compose it, Na and CI. They are nevertheless distinct 
and invariable as well as new. This distinction between the varia- 
bility of living matter and the constancy of non-living matter 
should be borne in mind later on when discussing some of the 
causes of variation. 



SECTION II — VARIABILITY THE BASIS FOR 
IMPROVEMENT 

Improvement is possible only where variability exists. The 
compound NaCl being constant, it would be impossible to pro- 
duce an improved variety of sodium chlorid, because the com- 
pound is always the same and cannot be had with other than its 
standard and invariable properties. Improvement in this com- 
modity is limited, therefore, to its mechanical form and cannot 
extend to its constitution. 

Living matter, upon the other hand, while possessed of defi-, 
nite properties, does not exhibit these properties always in the 
same degree, and observation and experience have both shown 
that profound changes may be made in either the form or the 
constitution of both plants and animals by the simple method of 
judicious combinations of desirable deviations. 

If there were no variability, and if living matter were as con- 
stant in its properties as is non-living matter, then we should be 
certain of what we already have, but no improvement would be 
possible. As it is, with variability everywhere, living organisms 
are both capable of improvement and liable to degeneration, for 
both are the logical consequence of variability. Man must there- 
fore work for what he possesses in the way of animals and 
plants, and they will serve him well or ill according to his knowl- 
edge and skill in dealing with their variations. 

Accordingly he cannot know too much about the variations that 
are likely to occur, — their nature, their extent, and the causes 
that control their appearance and determine their permanency. 



lO VARIATION 

He cannot know too much about life and its vicissitudes, about 
living things and what they do. 

An animal is born into the world. Its energies are first 
devoted to nutrition and growth. It builds its own machine 
and builds it quickly out of materials lying close at hand. In 
good time it is finished and all its energies are at a maximum. 
It seems like a stable thing that must live forever. But repro- 
duction occurs, securing a succession of its kind. One after 
another of its faculties fail, and its condition is again reduced to 
that of bare existence, with youthful recuperative powers gone 
forever. By and by some vital function fails. Then life goes 
out ; the organism breaks down and returns its elements to the 
inorganic world. Such is the brief history of a bit of matter 
temporarily endowed with life, — fleeting as a breath; any 
service it may render us must be caught in the passing. 

SECTION III — NATURE OF VARIABILITY 

The exact nature of variability is a most obscure subject, 
and one that cannot be fully comprehended in the present 
state of knowledge. Whether the distinctions between living 
and non-living matter will always remain as marked as they 
now seem to be, only future discoveries will determine. We 
have as yet only touched the fringe of this great subject, but 
enough is known to enable us to begin to penetrate some of its 
mysteries. 

At least two general principles may be laid down in the 
present state of knowledge without much chance of error : 

1. That all characters of plant and animal life, whether struc- 
tural or functional, are exceedingly variable. 

2. That ordinary variation is the result of a change in the 
relations between a number of associated characters through the 
deviation of one or more of the members, and not the introduc- 
tion of an absolutely new character. 

We speak loosely of " introducing new characters," but in 
truth improvement consists, not in the introduction of absolutely 
new characters, but in the intensifying of desirable old ones and 
the subordination of those that are undesirable. For example, 



VARIATION IN GENERAL I i 

when we undertake to improve the quahty of wool we hmit our 
attempts to the sheep, with which wool bearing is a natural 
character. Whether the horse or the hog could be made to grow 
wool is a question. If the hen could be made to produce milk 
or the cow to grow feathers, that would be the introduction of 
a new character in the strictest sense of the term. 

But nothing similar to this has ever been accomplished by man. 
The particular group of characters that constitutes a given species 
appears to be strangely fi.xed, and improvement seems to con- 
sist in changing the relations of these characters among them- 
selves rather than in the introduction of new members. How 
this particular grouping arose originally and how a new member 
(character) might be introduced are questions for the student of 
general evolution. They are questions, moreover, upon which the 
present state of knowledge sheds little light, and, so far as is 
known, the study of the practical breeder is limited to methods 
of dealing with groups of characters already associated and con- 
stituting well-marked types and forms. 

SECTION IV — MEANING OF THE TERM "CHARACTER" 

This is a much-abused term, loosely used in a variety of mean- 
ings. For example, when an individual differs slightly from 
another we say he has different characteristics. What we really 
mean is simply that his characters differ in their development, 
not that he has different characters. His bone is not so round 
or his hock so crooked ; the crops are not so full or the milk so 
rich ; the eye of the potato is not so sunken or the color of the 
fruit so high in one specimen as compared with another, and 
we say loosely that the characters are different. 

Now the truth is the characters are not different in kind but 
only in degree and proportion. We say of one horse that he has 
speed and of another that he has not speed. The fact is that 
they both have some speed, but only one has enough to attract 
attention and be worthy of remark. This use of terms, unfortu- 
nate as it may be, is probably too common to be changed ; indeed, 
the mere use of terms is of less importance than a clear compre- 
hension of the facts. 



1 2 VARIATION 

The term ** character " is employed in this text to designate one 
of those details of form or function which, taken together, consti- 
tute a well-marked group of animals or plants more or less closely 
related by descent, and this is the only sense in which the term 
oueht to be used. Thus the color characters of the horse are 
black, bay, brown, gray, etc., but not red, green, or blue, although 
these characters are not unknown to the animal world, being 
common with birds. 

Used in this sense, a " character " belongs primarily to the 
race or group of which the individual is a member. It is there- 
fore not peculiar to any particular individual and is in no sense 
personal property. Thus not only the color of the coat but the 
form of the body, the peculiar function of any of its organs, as in 
milk production or the secretion of poisons, any special mental 
attitude or intellectual function, or even a particular crook of 
limb or special body marking of any kind that runs commonly 
through the groups, is properly spoken of as a racial character. 
Those characters do not come and go, but on the contrary they 
remain with the race indefinitely. The individual horse, for 
example, will be marked by one or possibly more of the color 
characters of his kind, — black, white, bay, etc., — but he will 
not be marked with characters not of his kind, as red, green, 
etc. From this we see that the individual is not so good a 
unit for study as is the group to which he belongs and the racial 
characters that compose it. 

Now the personality of the individual so strongly impresses 
us that we instinctively regard him as an actual unit, and we 
speak loosely of his characters as if they were personal property 
peculiar to this individual alone, whereas he possesses nothing 
that is not common to his race. His differences are in degree, 
not in kind. 

What we mean to designate in the individual is the particular 
combination of racial characters that make up his personality, 
knowing perfectly well that the characters of all individuals within 
the race are racial characters and no other, and that every indi- 
vidual that may ever arise by descent will be limited as to his 
details to some combination of the characters of his race. Now 
the characters of any race are so many, their deviations are so 



VARIATION IN GENERAL 



13 



wide, and their power to move independently of one another is 
so great that, according to the doctrine of probabiUties, an ahnost 
infinite variety of combinations is possible. Hence no two indi- 
viduals are ever likely to be identical. We thus arrive at the 
conclusion that the proper study of the breeder is not so much 
the individual as it is the normal characters of the race to which 
he belongs. 

SECTION V — DOMINANT AND LATENT CHARACTERS 

The race as a whole clearly possesses more characters than can 
ever be utilized in the visible make-up of any single individual. 
Among" all the colors of horses, but one, or at most two, can be 
found in any special instance. The race is therefore a kind of 
composite of all the individuals that compose it, or, more properly 
speaking for purposes of study, it affords a wide assortment of 
elements out of which individuals are composed. 

The individual transmits the characters of the race. If the 
group of characters constituting a species is larger than that 
constituting an individual, as with color among horses ; and if 
an individual may transmit a character which (apparently) he does 
not possess, and experience shows that he does, then it follows 
that the individual is in actual possession of more characters than 
those directly involved in his visible make-up. 

For example, the offspring of two black horses will likely be 
black, but it may be bay, brown, or any other color characteristic 
of the horse kind. It is safe to say that it will not be red, green, 
or blue, because these colors are known not to belong to the 
horse kind, though all are freely found in nature. 

Milk secretion is confined to the female sex, yet a bull whose 
dam is a heavy milker will transmit milking cjuality almost as 
successfully as will a cow. In this instance the male transmits a 
quality that he does not apparently possess and that could not 
become functional in his case. 

From this we infer that the individual, whatever his particu- 
lar make-up, transmits all the characters of the race, and none 
other ; and that he is therefore possessed of all the racial char- 
acters of his kind in some degree visible or potential. From 



14 . VARIATION 

this we conclude that the apparent make-up of the individual 
depends upon the particular characters that happen to be 
strongest, that is, most highly developed in his case, but that 
he is in actual possession and may transmit any and all the 
characters of the race to which he belongs, but no other. 

We now arrive at the distinction between dominant and latent 
characters, which is as follows: Those characters that are prom- 
inent in any individual are said to be dominant with him because 
well developed and plainly evident, and all other racial charac- 
ters are said to be latent because not evident, although they are 
known to be present from the fact that they are transmitted to 
the offspring, often becoming the dominant characters in future 
generations. 

The term "latent" should not convey the impression of 
hidden or lurking characters, but rather undeveloped possibil- 
ities of the race within the individual in question. With this 
conception the student will be saved much mental confusion 
when dealing with heredity and reversion. 

Elementary characters. In a biological sense the ultimate 
unit of variability, therefore, must be something less than the 
racial characters which we have been discussing, because they 
themselves are complex rather than simple. We speak of the 
leg of a horse or the quality of milk as a whole. Even if we 
narrow the point to the conformation of the hock or the propor- 
tion of fat, we yet have characters clearly made up of parts. 
The hock is an exceedingly complex structure, and seven, pos- 
sibly nine or ten fats and oils are found in the fat of milk. 

As almost unlimited color effects are made up by few pri- 
maries in different proportions, and as all ordinary materials are 
made up of a few chemical elements in different combinations, 
so in all probability if we could make the ultimate analysis we 
should find that all these characters are made up of definite liv- 
ing units, that we may call, for want of a better name, elementary 
characters. 

These elementary characters have received many and various 
names. They are the stirp of Galton, the biophors of Weismann, 
and the physiological units of biologists generally. In general 
they are the smallest conceivable living units, comparable with 



VARIATION IN GENERAL 



15 



the molecule of chemical compounds. Such elementary charac- 
ters are supposed not to be variable except as they effect dif- 
ferent combinations among themselves. 

SECTION VI— THE UNIT OF VARIABILITY 

The unit of variation is therefore not the individual but the 
racial characters that constitute the particular, group, and that 
run down the line of descent like the strands of a rope and out 
of which individuals are made up, — some with one combination, 
others with another, after the fashion of threads in a fabric, 
forming patterns here and there, now of one design now of 
another, as they wander apparently aimlessly here and there. ^ 

It is evident, however, that the actual basis of character devia- 
tion is sometimes exceedingly complex. Milk secretion, for 
example, while limited to certain animals and confined to the 
female sex, is properly recognized as a distinct character ; yet 
its successful functioning depends upon a variety of considera- 
tions, — the general health of the body, the nervous tempera- 
ture of the individual, the power of the stomach to provide large 
quantities of prepared food, the ability of the kidneys to do 
their work, and the power of every organ in the body to dis- 
charge its function successfully and fully under heavy strains. 
All these are as important to successful milk production as 
are large and active milk glands, and an accident at any point 
will cause deviation in milk yield either as to quantity or quality 
or both. 

Deviation in color, on the other hand, may be due to presence 
or absence of pigment, which may be regarded as a chemical 
substance secreted at a single point. In this and in similar 
cases the actual basis of deviation is simple and readily detected. 
From this it will appear that the ultimate seat of variation, 
whose fluctuations are responsible for character deviations, may 
be exceedingly difficult if not impossible to identify. 

1 The unit of variability must not be confused with the unit of selection : the 
latter, of course, is the individual. We cannot separate his characters, but must 
take him as he is, for better or for worse ; but we must do so fully realizing that 
each of his separate characters has an identity of its own, so that the unit of vari- 
ability is far within the necessary unit of selection. 



1 6 VARIATION 

It has been assumed that the ultimate unit of organized 
beings is the cell. This is true in a structural sense only, for 
there is positive evidence that the cell is itself made up of 
various and distinct elements capable of somewhat independent 
action in both cell division and growth. The content of a cell 
is not to be regarded as a mass of amorphous protoplasm to be 
halved or quartered by chance, but on the contrary it is an 
organized body with a distinct difference between the nucleus 
with its definite number of chromosomes (the supposed seat of 
the physiological units that give character to its activities) and 
its surrounding cytoplasm or food material. 

Again, a whole group of similar cells may constitute a special 
organ (liver, kidney, or heart), discharging a highly specialized 
function quite different from that of any other portion of the 
body. This colony of many cells discharging the same function 
appears to move together, thus constituting a kind of functional 
unit larger than and quite distinct from the ultimate physio- 
logical units that must reside within the cell. 

Correlated variation. Still again, it is found in practice that 
occasionally whole groups of characters seem to be so correlated 
as to move together, so that having found one we may reason- 
ably expect to discover the other. Familiar examples of this 
are found in nearly all cases of reversion. For instance, a white 
calf among Devon cattle will almost certainly show black or 
brown points (ears, nose, and legs), while a white shorthorn will 
not. The one is a case of reversion to the ancestral color of the 
breed, — the wild cattle of Britain; the other is simply the 
appearance of one of the normal color characters of the race. 
In increase of numbers of parts there is some tendency to repeat 
a whole group, as in cases of " double hand." ^ 

The same tendency for many distinct characters to move 
together in groups is found in cases of so-called " sports," in 
which we instinctively recognize something more than ordinary 
variation. 

These instances of grouping of characters normally independ- 
ent in such a way as afterward to move together is to be dis- 
tinguished from such variation as is involved in extreme milk 

1 See under Meristic Variation. 



VARIATION IN GENERAL 



17 



production, in which results arc to be ascribed rather to fortui- 
tous variations among independent units than to anything like a 
linking together of the separate characters involved. 

The ultimate unit. The student must maintain a clear vision 
as to distinctions of this sort. From the biological standpoint 
we accept as the unit of variability the ultimate physiological 
units that must reside within the cell ; for purposes of everyday 
use, however, we assume as a unit that detail of form or function 
that is important to the breeder, understanding perfectly well 
that, considered physiologically, it doubtless consists of a num- 
ber of ultimate units which, like the elements in a chemical com- 
pound, are entirely capable of other and distinct combinations. 

To repeat, we may assume either one of these conceptions as 
the unit for study according to the purpose in hand. In the 
text the word " character " will be used to denote that detail of 
(racial) structure or function which is important to the farmer 
and to this study. The character will be considered as the 
practical unit of variation, knowing perfectly well that the ulti- 
mate unit of variability lies much farther back in the constitution 
of the protoplasm itself. When this is in mind the terms " ele- 
mentary character," "physiological unit," or some equivalent 
term will be used. 

Whatever the situation, the student must not consider the 
individual as the unit of variability or he will come to grief both 
in study and in practice, nor should he become confused by 
those occasional and remarkable correlations of characters that 
suggest a unit of variability unduly large. 

SECTION VII — DISTINCTIONS AS TO KINDS OF 
VARIATIONS 

In the critical study of variation it is necessary to observe 
certain distinctions that are often overlooked, resulting in more 
or less confusion as to what is really involved in the term 
"variation." 

Variation quantitative or qualitative. The first c[uestion that 
should arise in the mind of the student touching any deviation is 
this : Is the difference one in degree merely (quantitative) or 



1 8 VARIATION 

is it a difference in kind (qualitative) ? For example, one horse 
is exactly like another, only larger : ' the difference is quanti- 
tative. Another is no larger, but he can draw more and has 
greater endurance : the difference is qualitative. One cow gives 
more milk than another : the difference is quantitative ; but a 
third gives better milk, and the difference is qualitative. One 
apple is larger than another of the same variety (quantitative 
variation), but another is different in texture and flavor (quali- 
tative variation). 

When, therefore, in the study of a racial character as repre- 
sented in the same or in different individuals it is found to have 
varied, the first question to ask and answer is this : Is the devi- 
ation one in kind or merely in amount ? Is it qualitative or merely 
quantitative .? Is the change to be regarded as one in nature or 
only in degree .'' If the student will carry these distinctions always 
in mind, he will avoid much needless confusion. 

Variation continuous and discontinuous. It is not to be assumed 
that variations differ from one another by infinitesimal increments. 
The differences may be infinitesimal (continuous variation) or they 
may be "discrete " (discontinuous variation). 

Darwin supposed, and it is commonly assumed, that variation 
is by nature continuous, and that new forms originate by the 
gradual accumulation of insensible differences through the agency 
of long-continued selection. This means that if all the individuals 
that ever lived could be assembled and so assorted as to bring 
nearest together those that are nearest alike, it would then be 
found that they would grade into one another by imperceptible 
differences, and that any gaps that might occur would be due to 
the effect of selection in blotting out intermediate forms. 

Now this is a hasty assumption, indicating in these days but 
a superficial acquaintance with the manner of variation. We 
cannot assume that all possible values in variable characters are 
presented ; indeed, we know very well that in many cases all 
possible values are not presented, and that some intermediate 
forms never arise. For example, peaches often give rise to 
nectarines, but there is a gap between the two that apparently is 
never filled. Darwin called an occurrence of this kind a "sport," 
as if it were an instance in which all ordinary laws were set aside, 



VARIATION IN GENERAL I9 

whereas it only shows that the variations of the peach are often 
discontinuous, with wide gaps representing spaces not filled by- 
variation. 

To get a full understanding of this ground the student must 
form a clear conception of the distinction between continuity and 
discontinuity as used in this connection. 

A man grows from childhood to maturity. In doing so he 
passes through all possible weights and heights between those of 
infancy and maturity. We cannot represent all these values by 
any of our units of weight or measurements because all numbers 
are by nature discontinuous. The only measure of continuity is 
a line, because a line, curved or straight, represents all values 
sensible and insensible between its two extremes. We can thus 
plot continuity, but we cannot measure it except by cutting it 
into sections and measuring it at stated points as if it were dis- 
continuous, ignoring the intervals. 

Changes of temperature are continuous, as are those of humidity, 
illumination, and all growth in the sense of extension in size, 
whether plant or animal. All motion, whether regular or irregular, 
is continuous because all intervening spaces are included. 

Discontinuity, on the other hand, implies vacant spaces not 
represented by values. The good singer goes abruptly from one 
note to the next, giving a discontinuous series of tones, while the 
unskilled vocalist slides up or down the scale, giving rise to a 
continuous series of tones in his effort to find the proper note. 
The latter is not music because the ear is not pleasantly affected 
by this confused jumble of sound waves arising from the inter- 
mediate tones. Good music consists of a series of tones not 
flowing into one another but cut sharply off and cast into a 
discontinuous series, striking the ear at intervals with sound 
waves that fit with mathematical precision. 

All number is by nature discontinuous. By fractions we attempt 
to bridge the space between contiguous units, as between i and 
2 ; but however small the fraction, there is yet a space, and a 
sensible and measurable one, between the fraction and the next 
unit. lyVfToTj- is not 2, nor will it ever become 2 this side of 
infinity by the addition of any number of nines to the numerator 
and ciphers to the denominator. It will constantly approach 2, 



20 • VARIATION 

but will never reach it, because definite number is discontinuous. 
This is why we can never accurately measure continuity except 
by a line, and this is why we cannot express in numbers the 
growth of an animal or plant, except approximately in terms of 
discontinuity. 

All chemical compounds are made up of elements in definite 
proportion. They are therefore discontinuous. We have H2O 
and H.2O.2, but no intermediate is possible, — this again for numer- 
ical reasons. Plants and animals generally are dimorphic, the one 
form being male, the other female : this is discontinuity. Some 
species are trimorphic or even polymorphic. The ant is either 
male, female, worker, or soldier, and though they all belong to 
the same species there are no connecting 
links in this discontinuous chain. 

Dimorphism without respect to sex oc- 
curs in many beetles, and is exceedingly 
marked in the common earwig,^ as shown 
in the accompanying diagram. 

The shape of this curve shows clearly 

Fig. I. Dimorphism iiius- ^hat here are two distinct forms of male, 

tiated: two types of the a large and a small one, living together 

common earwig. B is and arising naturally out of the common 

more common than A, . , • , ^ • , t , 

, ,, . . mass, yet showmg almost no mtermediates. 

and the type is more pro- ' ^ => 

nounced, but there are Students of breeding familiar with the 
almost no intermediates, older types of Hereford will recall that the 

— After Bateson i i ■, . ■,• i--^ii,j_ ^• 

breed was almost dmiorphic m that two dis- 
tinct types tended to appear with singular perverseness, refusing 
either to blend or to undergo modification. There was the old, 
large, solid-bodied, thick-meated, deep-ribbed type, ideal except 
as to lateness of maturity ; then there was also the pony-built 
type, — short in the barrel and lacking in depth behind, though 
well proportioned in front. 

The shorthorns are almost polymorphic in possessing not one 
but a variety of types, each standing out with extreme distinct- 
ness and not readily merged. 

The more the matter is examined the more it will be seen that 
strange and unaccountable gaps are found everywhere. Many a 

^ Bateson, Materials for the Study of Variation, pp. 36-42. 




VARIATION IN GENERAL 2 1 

breeder has spent his life and his substance in the vain attempt to 
produce a desired intermediate between two forms, either one of 
which are easily secured. The question arises, therefore, Are some 
intermediates impossible ? Can we bridge the space between the 
nectarine and the peach ? between the apricot and the plum ? 

With all these examples before us, we see at once that to pro- 
ceed upon the theory of continuity is a gratuitous assumption 
not borne out by facts. Force and physical agents generally seem 
to be continuous in their different manifestations, shading one 
into another with imperceptible gradations ; but organized matter, 
living or non-living, seems to be constructed upon the plan of dis- 
continuity, in which case we may expect to find differences that 
are easily perceptible, and should not be surprised at the appear- 
ance of wide spaces between nearly related forms or at these 
remarkably distinct gaps that often occur between a standard 
form and its offset, which Darwin called a " sport " and which we 
in these days call a " mutant." 

With this view of the case, we should not expect to find all 
nature united by imperceptible gradations, even providing all living 
beings past and present could be assembled and assorted according 
to nearest resemblances. Realizing the discontinuous nature of 
all chemical combinations, living or non-living, we should expect to 
find notable gaps representing spaces not taken by any possible 
form, and appearing quite independent of any selective process. 

This distinction is exceedingly important at the outset of this 
study. If all variations are continuous, then all shades of differ- 
ence, however minute, may be expected to occur naturally, and 
we may hope to secure them by breeding. If, however, some 
variations are discontinuous, then for these characters minute 
gradation is impossible, and we may expect descent to follow along 
certain lines only. 

Most of the conditions of life are without doubt naturally con- 
tinuous in their variations. This is certainly true of temperature, 
moisture, light, and food. Discontinuity must therefore arise from 
within, and is evidently connected with the nature of organisms. 
This is not difficult to appreciate when we recall the essential 
discontinuity of all chemical compounds or other organizations 
built upon the basis of distinct units. 



2 2 VARIATION 

The student must not therefore assume the possibihty of inter- 
mediate gradations and insensible differences when deahng with 
biological phenomena. Many of these differences are essentially 
and necessarily discontinuous. It remains to discover which 
these are and to discover the bearing of discontinuity upon the 
results to be accomplished by selection. 

If all variations were continuous we might hope to be able 
theoretically to accomplish any desired result and secure any 
desired shade of difference by selection ; but if not, then there 
will remain notable gaps that cannot be filled. The natural corol- 
lary of all this is that we can accomplish by selection almost any 
desired shade of result with those variations which are by nature 
continuous, but that with those variations which are by nature 
discontinuous, our efforts in this respect will be limited. 

Distinctions arising from the nature of the characters involved. 
Having determined whether the deviation is quantitative or quali- 
tative, continuous or discontinuous, we next inquire into the real 
nature -of the variation as it affects the organism. Manifestly 
this depends upon the character or characters involved. 

Those concerned with form will, in their deviations, give rise to 
morphological differences. On the other hand, deviation in char- 
acters distinctly functional will give rise to differences in organic 
activity without regard to form. 

Accordingly four distinctly different kinds of variation are 
recognized : 

1. Morphological, relating to differences in form or size. By 
nature they are always quantitative, but may be either continuous 
or discontinuous. 

2. Substantive, relating to differences in quality of the struc- 
ture as distinct from mere form or size. By definition they are 
always qualitative and generally, if not always, continuous. 

3. Meristic, relating to deviations in pattern, especially as to 
repeated parts, as in extra fingers and toes, doubling of petals, 
stooling of grain, etc. Variations of this kind are either quanti- 
tative or qualitative, generally the former, but are of necessity 
discontinuous. 

4. Functional, relating to deviations in the normal activity of 
the various organs and parts of the body or the plant, such as 



VARIATION IN GENERAL 



23 



muscular activity, glandular secretions, etc. They are either 
quantitative or cjualitative, continuous or discontinuous, though 
rarely the latter. 

A clear understanding of these distinctions is necessary to an 
intelligent study of the nature and causes of variation. Accord- 
ingly enough attention will be given to each to acquaint the 
student with the way in which variation behaves, partly for its 
own sake and partly as preparation for careful inquiry into 
methods of dealing with deviations in those plants and animals 
that we have domesticated and appropriated to our use, and 
which we would see still better adapted to the purposes of man. 

Summary. Variability is the universal rule among living 
beings. Literally no two are alike. The differences extend to 
all characters and to the most minute particulars. Non-living 
compounds exist in definite proportions, and their qualities are 
constant, not variable. Variability is the only basis for improv- 
ment. No improvment is possible, in the strictest sense of the 
term, with respect to inorganic compounds, but living matter being 
variable is capable of change and therefore of improvement. 

Variation consists not in the introduction of new characters 
but in different proportions or relations among the old ones. 
All characters are racial, and all individuals actually possess all 
the characters of the race and none other. This is shown by the 
characters that are transmitted to the offspring. 

The unit of variability is in no sense the individual, though he 
must be accepted as the unit for selection. The real unit of devia- 
tion is the racial character, but back of that, in a biological sense, 
lie the elementary characters or physiological units, whose vari- 
ous combinations constitute racial characters. 

Variation is both quantitative and qualitative, both continuous 
and discontinuous, and these distinctions should be clearly in 
mind at all times. 

Special Exercises 

Prepare a list of variations that are (i) quantitative, (2) qualitative, 
(3) morphological, (4) substantive, (5) meristic, (6) functional, (7) con- 
tinuous, (8) discontinuous. 



24 VARIATION 

ADDITIONAL REFERENCES 

Animals and Plants under Domestication. By Charles Darwin. 
2 vols. 

Discontinuous Variation. (An example.) By E. R. Saunders. Pro- 
ceedings of the Royal Society, LXII, 11-25. 

Origin of Species by Means of Natural Selection. By Charles 
Darwin, i vol. 

Theory of Organic Variation. By H. S. Williams. Science, VI, 

73-84. 

Type, How Fixed. (On genetic energy of organisms. Is variability and 
not permanency the normal law of organic life ?) By H. S. Williams. 
Science, VII, 721-729. 

Variation and Some Phenomena connected with Reproduction 
AND Sex. By Adam Sedgwick. Science, XI, 881-894, 923-930. 

Variation Discontinuous. (Study of a recent variety of flatfish.) By 
H. C. Bumpus. Science, VII, 197. 

Variation in Plants. (A study of the portions of a leaf on which chlo- 
rophyll is found.) Experiment Station Record, XIII, 423. 

Variation in Trillium grandiflorum. (A record of the variations 
observed in 185 cases.) By H. W. Britcher. Maine Experiment 
Station Bulletin No. 86, pp. 169-196 ; also Experiment Station Record, 
XIV, 634. 



CHAPTER II 

MORPHOLOGICAL VARIATION 

Morphological variation has reference to differences in form. If 
two or more individuals possess the same structural characters and 
if they have all attained the same relative development, then the 
different individuals will differ only in size ; but if the characters 
have not attained proportional development in the different indi- 
viduals, then we shall note differences in form independent of 
mere size. This is the simplest of all forms of variation and is 
the one chiefly in the mind of older biologists, even leading to 
the mistake of supposing that evolution is essentially a study in 
morphology. 

The cause of morphological differences may lie in extremely 
favorable or unfavorable conditions of life, especially as regards 
food and climate, affecting different characters differently, or 
they may arise from internal and constitutional causes, as in 
giants and dwarfs, or in such extreme differences as in the mul- 
berry leaves shown in Fig. 2. 

Instances of morphological variation are so common and so 
easily noted as to scarcely require mention. Two apples are 
exactly alike except that one is larger than the other. It is a 
clear case of morphological variation. In this instance there is 
no difference in the characters of the two individuals except that 
cell division and growth have proceeded farther in one case than 
in the other. Aside from this they are identical. If two stalks 
of corn or if a number of pigs, sheep, cows, or horses are exactly 
alike except as to size, then their differences are cjuantitative 
only, and the effect is morphological merely. 

Again, two horses are of the same breed, — that is, possess the 
same characters, — but their characters are not equally, that is, 
proportionately, developed. In one the leg is longer, the hock 
shorter, or the face wider between the eyes. These differences 

25 




Fig. 2. Morphological variation illustrated : different forms of mulberry 
leaves picked from the same tree on the same day 



26 



MORPHOLOGICAL VARLATION 27 

are all quantitative and morphological, but they influence form 
rather than size as a whole, because their development is not 
proportional one part with another. 

Variation seldom simple. Instances of the above kind are, 
however, extremely rare. Variation is so common that other 
differences generally accompany those of form. The two apples 
may differ in color, flavor, or texture as well as in size, in which 
case substantive variation has also occurred. One of the horses 
may have an extra rib, one of the pigs a solid hoof, or one of 
the sheep more fibers of wool to the square inch, in which case 
meristic variation is present. The pulse of one of the horses 
may be faster than that of the other, or the milk of one cow 
may be richer in fat, showing functional deviation. 

And so it is in practice that two or more forms of variation 
may be and likely will be found present in the same individual. 
But however that may be, all differences in form or size are 
regarded as morphological, no matter what other differences 
may be found, and it is important that the student early form 
the habit of distinguishing clearly between the different kinds 
of variation present, even in the same individual. 

The limits of size. Every species has a general average of 
size to which most individuals closely approximate. A few, how- 
ever (giants), greatly exceed this size, and others (dwarfs) fall 
far short of it. All investigators agree upon the conclusion that 
this difference in size is due to the number and not the size 
of individual cells ; in other words, size is dependent upon the 
energy of cell division.^ This energy is exceedingly active in 
youth, gradually decreasing to zero at maturity, except as to 
certain parts (reproductive organs, skin, and sometimes the 
teeth and horns). In most species accident to a part will stim- 
ulate cell division, leading to a more or less successful regenera- 
tion. For the most part, however, cell division does not proceed 
rapidly after maturity, and the limit of its activity is in general 
the limit of growth. Giants therefore represent excessive cell 
division above the normal, and dwarfs, arrested development, — 
an abnormally early cessation of cell division. 

1 Wilson, The Cell in Development, pp. 388-394. 



28 VARIATION 

The causes involved in this abnormal behavior of the cell in 
division are exceedingly obscure. They are certainly sometimes 
connected with food and care in early life, and no doubt they 
are often constitutional. Every stockman knows about the 
stunted pig, calf, or colt, and that it sometimes, but rarely, 
recovers; that is to say, cell division once checked does not easily 
return to the normal rate. The trait, however, easily becomes 
constitutional and hereditary, for whole families (strains) become 
undersized and others as much above the medium. 

Energy of growth not to be confused with bodily or func- 
tional activity. While the larger animal of his kind, whether 
it be the individual or the strain, represents the greater energy 
of cell division in body building, it by no means follows that 
the body when built will possess a greater degree of activity 
than will its normal or smaller neighbor ; indeed, the opposite is 
likely to be true, because the larger body works at greater dis- 
advantage, having greater inertia to overcome and more dead 
weight to carry about. This is eminently true of all animals 
whose service involves transporting the body from place to 
place, as among horses. It is manifestly impossible for a heavy- 
horse to equal a light one in speed without the expenditure of 
far more power in doing it. This is not only because of the 
extra weight but because of mechanical disadvantages as well. 
In activities not involving motion this difference in size, within 
reasonable limits, does not exist ; small men, for example, are 
doubtless no more and no less intellectual than are large ones. 

Importance of morphological variation. Next to those of color, 
differences in size are the most noticeable of all variations; but 
they are by no means the most significant, and their importance 
is likely to be greatly overestimated. Except in a few instances, 
as with draft horses, mere size is of far less consequence than 
is commonly supposed. 

Generally speaking, it is some quality other than bulk that 
determines value, and it will be fortunate for breeding when the 
popular notion that " the biggest is the best " shall have passed 
away. The largest apple is not the best for eating, nor the 
largest bull the best for breeding purposes. However, this does 
not free the student and breeder from considerations of size. 



MORPHOLOGICAL VARIATION 



29 



because extremes both ways are in most cases to be avoided, 
and the highest excellence and the most reliable breeders will 
commonly be found among the individuals of medium size. 

Differences in form, arising from relative inequality in devel- 
opment of structural parts, are of more consequence than are 
differences in mere bulk, in which development has been pro- 
portional. This is especially true in horses, in which differences 
in relative development of structural parts may seriously affect 
the appearance or interfere with the action of the individual. 
And so it is that, while morphological differences are of far 
more significance to the student of general evolution than they 
are to the farmer, they yet constitute a phase of variation not 
to be overlooked by the student who is interested in the improve- 
ment of domesticated forms. 

ADDITIONAL REFERENCES 

Darwiniana. By Asa Gray, i vol. 

Darwinism. By A. R. Wallace, i vol. 

Expression of the Emotions in Man and Animals. By Charles 

Darwin, i vol. 
From Greeks to Darwin. By H. F. Osborn. i vol. 
Lamarck: His Life and Work. By A. S. Packard, i vol. 



CHAPTER III 

SUBSTANTIVE VARIATION 

Substantive variation has reference to differences in quality 
as distinct from form or size. It regards the composition or 
make-up of the body or its members, and refers to the constitu- 
tion, or inherent nature, of the organism. 

Everybody recognizes differences in muscles, whether firm 
and strong, or soft, flabby, and weak. We distinguish the bone 
of a horse as dense or as soft, porous, and spongy. The horn 
of the hoof is hard and tough or soft and " shelly." 

Meat is fine in grain and high in flavor or coarse in grain and 
lacking in quality.^ It is either juicy and rich or dry and taste- 
less. The gamy flavor of wild meat, both of mammals and birds, 
is especially tasteful to the huntsman, and whether due to breed- 
ing or to feed, it is certainly characteristic of wild life everywhere. 
No two cuts of meat are alike, whether wild or tame, and these 
differences are so pronounced as to be commonly recognized ; 
indeed, language abounds in adjectives descriptive of differences 
in quality of food stuffs. 

At one time milk was sold on the quantitative basis only, but 
now the per cent of fat is the basis of value. The intelligence of 
an animal or of a man depends less upon the size and weight of 
the brain than upon the quality of the brain matter and the 
depth of the convolutions. 

One apple is sweet, another is sour, and still another is insipid. 
One fruit is highly flavored, another is tasteless. The sugar of 
beets, of cane, and of maple is the same ; but the two former are 
simply sweet, while the latter is accompanied by a highly volatile 
ether that adds a peculiarly delicious aroma.^ 

1 Pigs fed heavily on cotton-seed meal make a pork strongly flavored with 
cotton-seed oil. See Grindley, Journal of Atnerican Chemical Society-, Vol. XXVII. 

2 Isolated by Kedzie, of the Michigan Agricultural College, from samples fur- 
nished by the author. 

30 



SUBSTANTIVE VARIATION 



31 



The sugar content of beets varies from 4 or 5 per cent to over 
20 per cent. It is also exceedingly variable in cane. Wheat is 
richer in protein than is corn, but both are variable, and corn 
has been bred with a protein content higher than that of wheat .^ 

Plants differ in their ability to withstand frost as do animals to 
resist disease. A single stalk of corn may remain fresh and green 
when all its neighbors have been killed. Certain individuals seem 
immune to particular diseases, and appear to be able to resist 
infection indefinitely. 

Color in general is based upon definite chemical constituents 
or upon the character of the surfaces presented for refraction of 
light. In either case it is a matter of inherent quality and is 
substantive. 

Importance of substantive variation. The significance of sub- 
stantive differences depends upon the instance. Speaking gen- 
erally, these differences are of high value. They are usually, 
though not invariably, correlated with efficiency, and in such cases 
they possess a utilitarian interest. 

A dense bone is better than a soft and fibrous one. Every- 
body prefers a good apple to a poor one ; we have a decided pref- 
erence for certain aromas ; the juicy, highly flavored steak is 
better than the dry, tough, and tasteless one. 

Color is a utility character among flowers. We buy them for 
their color, their form, and their odor. They have no other value, 
and of these characters their coloring is of the most importance. 

Color, however, is in general the most deceptive of all charac- 
ters, — deceptive because it is striking and because we greatly 
prefer certain color effects over others, even though not correlated 
with utility. We carry this preference beyond reason. A red 
apple will sell for more than one of any other color ; yet we buy 
an apple not to look at but to eat ; and no one has shown a cor- 
relation between color and quality in fruit. 

Horses with white skin are proverbially subject to certain 
diseases. For this and other reasons color has no little signifi- 
cance in horses, but among cattle it has practically no meaning 
whatever ; and yet how decidedly do color markings figure in 

^ The lowest protein content discovered in the breeding experiments at the 
University of Illinois up to date (1907) is 6.13 per cent, and the highest is 17.79. 



32 



VARIATION 



many score cards for pure-bred animals ! Now the facts are that 
a cow is kept for what she can do, and there is nothing inherent 
in mere color that is indicative of her ability to convert feed into 
either milk or meat. She is therefore neither better nor worse 
for her color except as it is an index of blood lines when she is 
to be used as a breeder. 

So striking are color differences, however, and so distinct are 
our preferences, that we instinctively follow our prejudices in this 
respect, quite regardless of more important considerations, until 
the whole fabric of breeding is interwoven with "fancy points" 
in the shape of color markings that greatly confuse the breeder 
in his attempts to select individuals for breeding purposes. 

To-day the majority of prize-winning shorthorns are either 
roan or pure white. Twenty-five years ago no breeder would 
have dared to show a roan animal, and if a white calf had been 
dropped in his herd he would have destroyed it at once and kept 
the matter as secret as possible, so strong was the red color craze 
following the American worship of Bates cattle. This craze, 
which was always groundless, cost the breed and their admirers 
dearly and checked by a decade or more its progress upward. 

Probably of all substantive variations color is, excepting among 
flowers and ornamental plants, of the least consequence to man ; 
yet the prejudice is with us, and the breeder who expects to sell 
his product must reckon with it. He should do it intelligently, 
however, realizing fully that individuals vary greatly in inherent 
quality quite independently of color. 

In general it may be said that substantive differences, though 
not so easily detected, are yet of far more significance to the 
farmer than are those of either form or size. 



CHAPTER IV 

MERISTIC VARIATION 

Meristic variation has reference to a deviation in the number 
or arrangement of repeated parts involved in the plan or pattern 
upon which any particular organism is built. 

A plant or an animal is not an amorphous lump of living 
matter. On the contrary, it is made up of parts, each of which has 
a kind of identity of its own, many of which arc similar, and all 
of which are definitely related and placed in some sort of orderly 
arrangement. 

Reflection discloses the fact that each organism is developed 
upon a specific plan, essentially different from that of any other, 
and that with most organisms the pattern is composed of a defi- 
nite number of similar parts more or less repeated. 

Thus the chicken has two legs, and the horse has four legs, 
that are more or less alike. The flower has many petals, the 
corn plant many leaves ; the spinal column is composed of vertebra 
very much alike, and organisms generally possess many parts 
that more or less closely resemble one another. 

From this it appears that the individual animal or plant is 
not a unit in respect to form, but rather that it is made up of 
many units, some of which are practical duplicates. Thus the 
idea of multiple parts in orderly arrangement {inerism) comes at 
once into the study, and variation in the number or character of 
these repeated parts (meristic variation) is a broad and compli- 
cated subject affording considerable insight into the nature of 
variation. Accordingly it is profitable to pursue it at considerable 
length, not so much for the material involved, which consists 
largely of abnormalities of no practical interest or value, but 
because no other phase of variation affords so much information 
upon the real nature of living matter and its adherence to or 
deviation from a definite plan. 

3J 



34 VARIATION 

SECTION I — SYMMETRY 

The central thought in all mcristic studies is symmetry, by 
which is meant that opposite sides of an organism possess parts 
that are either identical or at least similar. Thus the petals upon 
one side of a flower are in most cases like those upon the oppo- 
site side, and the blossom is made up of a number of similar parts 
very much alike and several times repeated.^ 

Among higher animals, however, opposite sides are similar but 
not identical, and here arises the distinction between radial sym- 
metry and bilateral symmetry. 

Radial symmetry and radial series. By this is meant that kind 
of pattern in which the separate parts are identical and each part 
is capable of replacing any other in the series. Common examples 
are the petals of most flowers (leguminous and the like excepted), 
the leaves and lateral shoots of plants, the capsules of many seeds, 
such as the apple, orange, etc., the rows of corn upon the cob, 
the parts of the sea urchin, the starfish, and the Jladiolaria 
generally. 

In all cases of this sort the individual parts could each replace 
any other part of the series. The pattern is therefore spoken of 
as one of radial symmetry, and the parts as members of a radial 
series. 

Bilateral symmetry. Among higher animals a different sym- 
metry is observable. While each side has its counterpart upon 
the other, yet there is a distinction between the right and the 
left sides and between the dorsal and the ventral surfaces. In 
such cases the parts while similar are not alike, nor could they 
replace each other. 

1 Symmetry is 7vcll-)iigh universal. All organisms arise through cell division in 
one or more planes, and some degree of symmetry is to be expected from the 
manner in which growth takes place. 

But symmetry is not confined to multicellular structures. Appendages consist- 
ing of single cells are frequently symmetrically placed, and many organisms, which 
are single celled and therefore microscopic, as diatoms, secrete a skeleton with 
regular markings as symmetrical as hoarfrost and quite as beautiful. 

All this is curious rather than valuable to the student of thremmatology who 
is interested in multicellular beings ; yet it all throws light on the method of life, 
and we are able to lay down the principle that symmeti^ is not only the natural 
corollary of development by cell division, but that it is also a general principle in 
living matter. 



MERISTIC VARIATION 35 

The right hand and arm are made upon the same plan as the 
left, but could not replace them because they would not fit ; the 
one is the reverse of the other. 

Reflected in the mirror the right hand seems to be the left, 
but it is an illusion, for the right side is the negative or optical 
image of the left with all its elements reversed. Hence a part 
upon the one side could not replace the corresponding part upon 
the other. It is its counterpart, not its duplicate as among leaves 
and petals. Thus we arrive at the distinction between the com- 
plexity of bilateral symmetry and the simplicity of radial symmetry. 
It is also significant that bilateral symmetry is characteristic of 
higher animal life, and radial symmetry of lower animals and plants. 

Dorsal and ventral surfaces. The fundamental fact at the 
bottom of bilateral symmetry is the distinction between dorsal 
and ventral surfaces, necessitating differences in the quadrants 
that are forced to work in opposition to each other.^ 

Indian corn and the grass family generally are as distinctly 
bilateral as is the horse or man, yet there is no thought of dorsal 
and ventral differences, and hence no distinction between right 
and left. 

For example, let the leaves of a corn plant and the arms of a 
man extend east and west. Then the north and south sides of 
the corn plant will be alike. Not so with the man. In the one 
direction (we will say the south) will be his spinal column and 
the general framework of the body ; in the other (to the north) 
will be his face, his nose, his eyes, and all the active external 
parts. Moreover his hands are made to oppose each other and to 
work together with this (the ventral) side of the body. There is 
therefore bilateral symmetry in one direction but not in the other. 

With the corn plant the case is different. It does not move 
from place to place, and it presents its plain sides indifferently 
to the world. Accordingly no distinctions similar to dorsal and 
ventral are possible.^ 

1 The word "opposition " is here used not in the sense of " antagonism " but 
as "placed opposite and working with"; as, The thumb is "opposed" to the 
other members of the hand, thereby making a working unit. 

2 None of these distinctions should be confused with homologous parts or 
with analogous parts, nor should the ideas be confounded. 

Homologous parts belong to two individuals, not one, and they are such as 
bear corresponding structural relations to their respective organisms, suggesting 



36 VARIATION 

Bilateral symmetry not complete. Curiously enough not all the 
parts follow the same plan as to bilateralism and symmetry. What 
has been said refers to paired organs standing on opposite sides 
of the body, as hands, arms, legs, eyes, ears, etc. 

Many organs not paired present curious facts to the evolu- 
tionist. The nose, for example, has no counterpart, but it stands 
on the median line and has a bilateral symmetry of its own, 
being made up of right and left halves. The liver and the heart, 
however, while consisting of right and left halves, are unpaired 
organs, placed not on the median line, but the one upon the right, 
the other upon the left. Each has a bilateral symmetry of its 
own, with distinct right and left sides, yet both are unsymmetric- 
ally placed. 

The stomach, on the other hand, is an unpaired organ lying 
unsymmetrically across the body, and its own bilateralism is not 
between right and left hut from front to back. The kidneys pre- 
sent the anomalous phenomena of paired organs with a bilateral- 
ism of their own but at right angles to that of the body, being 
also from front to back. 

Longitudinal symmetry and linear series. Inasmuch as all 
growth is by cell division, we might expect longitudinal symmetry 
as well as lateral symmetry. Owing, however, to the definite 
relations of both animals and plants to the external world, it is 
not much developed, and there is but a suggestion of longitudinal 
symmetry to be found in either plant or animal forms. 

Most plants are both geotropic and heliotropic ; that is, one 
part goes down into the earth in response to gravity and the 
other upward toward the light and against gravity. This makes 

common descent. Thus the leg of a man is homologous with that of a horse or a 
bird, because of structural resemblances. In the same sense his arm is homolo- 
gous with the fore leg of the horse or the wing of a bird. 

Analogous parts are such as serve the same purpose in different organisms 
though structurally distinct. Thus the flipper of the whale, which is a modified 
hand, is analogous to the fin of a fish, and the gill of a fish is analogous to the 
lung of a mammal, because it serves the same purpose, though there is no struc- 
tural relation between the two. 

The homologue or the analogue of a part is therefore to be found in another 
individual and of a different species. Symmetry, on the contrary, with its corollary 
of multiple parts, refers to individuals taken singly and to the interrelations of 
their parts. 



MERISTIC VARIATION 37 

the two extremities at once very different, and forestalls the 
development of any very pronounced symmetry longitudinally. 

Animals in their locomotion establish different relations at their 
opposite extremities, thus preventing exact symmetry in this direc- 
tion, and yet reminders of inherent tendencies toward universal 
symmetry are constantly encountered. Long worms, for example, 
though distinctly different at the extremities, are yet compo.sed 
of rings very much alike throughout most of their length, even 
permitting locomotion backward with considerable facility. 

Longitudinal division, however, with or without corresponding 
symmetry, is everywhere found both in plant and animal life, espe- 
cially in the latter, and linear series of similar parts present as 
many opportunities for variation as are afforded by radial series 
either with or without bilateral symmetry. Thus the rings of 
worms, the vertebras and the ribs of the body, the joints of the 
fingers and of insect parts, — all these are fertile sources of 
meristic variation. 

Homoeosis in meristic variation. This is a form of variation in 
which one part assumes the characters or appearance of another, 
usually quite distinct. It is a frequent accompaniment of meristic 
variations. For example, an extra vertebra may be found in the 
dorsal series, increasing the number by one, — all normal. This 
is meristic variation of the simplest kind, with no homoeosis. 

On the other hand, it may be situated at the front of the dor- 
sal series and partake somewhat of the character of a cervical 
(forward homoeosis), or it may be located at the rear of the dor- 
sal series and in many respects resemble a lumbar (backward 
homoeosis). 

This posterior dorsal vertebra may bear a rib that is bifurcated 
at the extremity, one branch effecting a union with the sacrum, 
the other floating, in which case there is doubt as to the real 
character of the additional vertebra, whether dorsal or lumbar. 

In much the same way misplaced organs are often found. A 
leaf may be seen growing from a fruit, an antenna may spring 
from an injured eye, or foot appendages may develop instead of 
those proper to the extremity of the antenna. 

All cases of this order, in which one organ through some dis- 
turbance assumes the character of another organ, are known as 



38 VARIATION 

homoeotic variations, and homoeosis of some sort is a frequent 
accompaniment of meristic variation in longitudinal series. The 
best instance of this is found in the petals of flowers which are 
recognized by botanists as modified leaves, and instances are not 
rare in which the specimen plainly shows the various transition 
states from leaf to sepal, sepal to petal, and petal to stamen. 

This tendency of one part to assume the character and dis- 
charge the functions of a neighboring part is an important phase 
of variation, throwing much light upon the general subject of 
development. 

With this introduction the student is prepared for the study of 
meristic variation somewhat in detail, in which he will find that 
while each species is built upon its own somewhat peculiar and 
definite pattern, yet this pattern is subject to many and profound 
alterations, and the organism is frequently able to exist upon an- 
other and much-distorted plan, all of which goes far toward enlight- 
ening the student as to the variations that may be expected in the 
organic world. Studies in meristic variation are useful to the stu- 
dent of thremmatology, not so much for their own sake as for the 
light they shed upon the nature and manner of variation. 

Examples of meristic variation. Examples of meristic varia- 
tion are to be found at every hand. In the doubling of flowers 
and the stooling of grain, in increased or reduced numbers of 
fingers and toes, in the four-leaved clover and the branching 
habit of many plants, — everywhere are seen alterations in the 
customary plan on which nature does its work. 

Fortunately an extended and valuable collection of meristic 
variations, mostly among animals, has been made by Bateson.^ 
He lists his data under 886 headings, each recording from one 
to several authentic cases. 

Equally complete data covering plants have not been collected, 
though it is among plants that meristic variation is most common. 
Indeed, it is so common and so evident that formal collection is 
hardly necessary. The student is therefore referred to plant life 
out of doors and to Bateson's collection for a fuller study of this 
important subject, a bare outline of which, as a guide, being all 
that is attempted here. 

1 Bateson, Materials for the Study of Variation [Macmillan & Co., 1S94]. 



MERISTIC VARIATION 



39 



SECTION II — MERISTIC VARIATION IN LINEAR SERIES 

Vertebrae. Among fishes and snakes variation in the number 
of vertebrae may be very great. In mammals it is smaller but 
yet distinct, as in the following examples, instances of which, 
according to Bateson, could be multiplied indefinitely. 

Erinaceous Europ.'eus (The Hedgehog) ^ 





No. 


Cervical 


Dorsal 


Lumbar 


Sacral 


Coccygeal 


Total 


1 


7 


14 


6 


4 


II 


42 


2 


7 


'5 


6 


3 


10 + 




3 


7 


i6 


6 


3 


9 + 




4 


7 


15 


6 


4 


12 


44 


5 


7 


15 


6 


4 


II 


43 


6 


7 


14 


6 


3 


9 + 




7 


7 


15 


6 


3 


II 0112 




8 


7 


15 


6 


3 


13 


44 


9 


7 


15 


6 


3 


12 or 13 





It will be noticed that i and 5 differ only in the dorsal region, 
which fact, however, affects the total, but that 4 and 8 differ both 
in the sacral and the coccygeal without affecting the total. 

Commenting on the phenomena of an additional lumbar or 
sacral vertebra, Bateson says : 

. . . There is a strong suggestion that (in cases of this kind) the num- 
ber of vertebras has been increa.sed by simple addition of a new segment 
behind, after the fashion of a growing worm ; the variation of vertebrae 
thus .seems a simple thing. But there is evidence of other kinds, which 
plainly shows this view of the matter to be quite inadequate. 

What this evidence is he proceeds to show by succeeding 
examples, a few of which are reproduced here : 

In a skeleton of Python tigris'^ (No. 602, Museum of the College 
of Surgeons) the vertebrae are normal up to the 147th inclusive. 
The 148th and 149th are, however, abnormally short from front 
to back, suggesting arrested development with imperfect separa- 
tion, although each vertebra bears a normal rib on either side. 

1 Bateson, Materials, etc., p. 103. 2 ibid. pp. 103-105. 



40 



VARIATION 



Passing backward in the same specimen, the i66th vertebra is 
seen to be normal on the left but double and bearing two ribs on 
the right, thus greatly crowding the ribs on that side. The 185th 
vertebra is reported in the same condition, both being doubled 
on the right side and single on the left (see Fig. 3). 

Following, Bateson ^ gives two examples of the reverse condi- 
tion, namely with duplicity on the left side, and another with 

duplicity on the right, showing 
clearly that meristic variation in 
one side of a bilateral symmetry 
may or may not involve the other 
side. 

Ribs. Variation in the dorsal 
region necessarily involves the 
ribs. Aside from this, all evi- 
dence goes to show that j^artial 
division of the ribs is much more 
common than is variation in the 
number of vertebrae. In man, 
for example, the cartilage is fre- 
quently divided for a considerable 
distance (1.5 in.) back from the 
sternum, often involving a real 
bifurcation of the rib itself. 
Homoeotic variation in vertebrae and ribs.^ These may be out- 
lined as follows (all in man, except as noted) : 

I. Cervical resembling dorsal : backxvard homceosis. The dis- 
tinguishing character of dorsal vertebrae is the bearing of ribs, 
but this character is often assumed by neighboring cervical, 
being common on the seventh and not unknown on the sixth. 
Of fifty-seven cases examined by Struthers, forty-two showed 
ribs on both sides and fifteen on one side only, showing a tend- 
ency to preservation of symmetry. The completeness of develop- 
ment ranges all the way from the merest rudiments (rare) to a 
perfect rib connected by cartilage to the sternum (also rare), the 
commonest form ending free or being joined by cartilage to the 
first true rib. 




Fig. 3. Meristic variation in vertebrae : 
double on right side. — After Bateson 



1 Bateson, Materials, etc., p. 105. 



2 Ibid. pp. 106-128. 



MERISTIC VARIATION 4 1 

2. Dorsal rcscnibling cervical : forzvard Jiovio^osis. Not so 
common as above, but Struthers^ describes a specimen in which 
the first pair of ribs is defective. On the left side the rib 
extends but two fifths of the way around, where it articulates 
with a process on the second rib. On the right side it joins the 
second rib about one inch beyond the tubercle. As seven nor- 
mal cervical vertebras are present in this specimen, it is to be 
regarded as a modified dorsal rather than an extra cervical assum- 
ing the characters of the dorsal, as in the preceding cases. 

3. Dorsal resembling lumbar. Frequently the twelfth rib 
in man is rudimentary, in which case the last dorsal vertebra 
assumes the form and general appearance of a lumbar. 

4. Lumbar resembling dorsal. Cases of a thirteenth rib are 
not unknown but are more rare than the reduction of the 
twelfth. 

5. Homceosis betiueen lumbar, sacral, and coccygeal. The last 
lumbar may unite on one or both sides with the sacral, in which 
case the lumbar develops processes to assist in the support of 
the ilium. On the contrary, the first sacral may remain detached, 
thus becoming practically a lumbar. Similar relations obtain be- 
tween the sacral and the coccygeal. 

A careful study of this whole subject develops the following 
facts : 

1. That an increase in the number of parts in one region may 
or may not affect the total number in the series. 

2. That consequently a change in number in one region may 
or may not be accompanied by changes in other regions of the 
same series ; that is, changes in the dorsal do not imply changes 
in either the cervical or the lumbar. 

3. That homceosis in vertebrae and ribs is confined to members 
contiguous ; that is, if a cervical resemble a dorsal, it will be that 
cervical lying next to the dorsal series. 

4. That the tendency is for an extra member to resemble 
somewhat the members of the next region ; that is, an extra 
dorsal is likely to resemble a lumbar or a cervical, if not to 
entirely replace it, suggesting that it arose at the end, and not 
in the middle, of the dorsal series. 

1 Bate.son, Materials, etc., p. 109. 



42 VARIATION 

5. That forward homcEosis in one region is not necessarily- 
attended by forward homoeosis in other regions of the same 
series. 

6. That in general (especially in man, where this has been 
most studied) forward homoeosis is attended by a total increase 
of the series, and backward homoeosis by a decrease. 

7. That an abnormality on one side may or may not be 
attended by a like abnormality on the other, though the tend- 
ency is strongly to the preservation of bilateral symmetry. 

8. That when one part resembles another it is the member 
lying contiguous ; that is, a dorsal vertebra will resemble a cer- 
vical or a lumbar, not a sacral, and lying between the stamen 
and the leaf are the petal and sepal and all intermediate grada- 
tions, either present or obliterated. 

Meristic variation in spinal nerves. Branches from the spinal 
cord emerge between the vertebrae, so that in general the sys- 
tem of spinal nerves is determined by the vertebras. Aside from 
this, however, the emergence of the branches varies greatly 
both in number and in conformation, even when the vertebrae 
are normal. 

Fiirbringer's ^ studies in birds show that the minimum num- 
ber of spinal nerves forming the brachial plexus (supplying the 
wings) is three, but in some species it rises as high as six. 
Moreover, in some instances the number varied from four to 
five zvithin a single species^ and in one (the pigeon) the varia- 
tion was from four to six. As might be suspected, the two sides 
are often differently supplied. For example, in one specimen 
(goose) " the plexus was formed on the right side by nerves xvi, 
XVII, xviii, and xix, while on the left side it received a strand 
from the xxth nerve in addition to these." 

Fiirbringer's tables show that in some specimens of the goose 
the wings were supplied by the nerves xv to xix, while in 
others they were supplied by the xviith to the xxth. In the 
dove the brachial plexus was formed by the xth branches of 
the spinal nerve in some specimens, by the xiith to the xvth 
in others, and in one case by the xith to the xivth as an 
intermediary. 

1 Bateson, Materials, etc., pp. 129-135. 



MERISTIC VARIATION 



43 



Herringham ^ dissected to their origin the nerves forming 
the brachial plexus in fifty-five human subjects (thirty-two fetal 
and twenty-three adult). Quoting from his work, Bateson says : 

The origin of the ulnar nerve was traced in thirty-two cases, fourteen 
being adults. It (the ulnar nerve) was found to arise in four different ways. 
Most commonly it arises from the vnith and ixth ; this occurred in twenty- 
three cases. With the vnith and ixth is sometimes combined a strand from 
the viith, as shown in five cases (four fetal, one adult). In three fetal 
cases it arose from the vnith only, and in one fetal and one adult case from 
the \iith and vnith. ... In several cases the branch from the vnith was 
much larger than that from the ixth, but the reverse was never met with. 

Similar conditions were found elsewhere with man, the gorilla, 
baboon, and chimpanzee, and the following principle was set 
forth : " Auj/ givett fiber may alter its position relative to the 
vertebral eolnmn, but xvill maintaiji its 
position relative to otJier fibers'' 

Homoeosis in insects and other small 
animals. The replacement of one part 
by another, while common among plants 
(modified leaves and stems), is compar- 
atively rare in animal life. It is, however, 
by no means unknown, and some striking 
examples are quoted from Bateson to 
show the remarkable manner in which a 
perfect part may arise in a most unusual Fig. 4. Homceotic variation 

1 1-1 .1 r 11 • 2 in sawfly: right antenna 

place, among which are the following -.^ , , r . 

^ ' ° ° normal; left antenna 

1. Specimens of sawfly (Cimbex axillaris^ in ^^^""S ^ ^°°*- ^ ^"^^ ^' 
,.,.,, r, . J J • ,, 11 r 1 enlarged. — After Bateson 

which the left antenna ended m "a well-formed * 

foot, having a pair of nomial claws and the plaiiiiila between them " 
(Fig. 4). Right antenna normal.'' 

2. A male bumblebee {Bonibiis vaiiabilis) taken in Munich showed the 
left antenna " partially developed as a foot," bearing " a pair of regularly 
formed claws like the claws of the foot." 

3. A male specimen oi Zygceiia Jilipejidulce "pos.sessing a supernumerary 
wing arising in such a position as to suggest that it replaced a leg" (Fig. 5). 
The extra wing was on the left side and projected from the underside of the 
body after the exact fashion of the leg, which was absent. The specimen 

^ Bateson, Materials, etc., pp. 135-13S. - Ibid. p. 147. 

^ Ibid. pp. 146-155. Professor Bateson vouches for the genuineness of this 
specimen, which he himself carefully examined, although it belonged to Dr. Kraatz. 




44 



VARIATION 




belongs to Mr. Richardson, and was examined by Professor Bateson as 
closely as was possible without removing- the hairs, to which the owner 
objected. It is well known that supernumerary wings may arise with the 
normal number of legs. In this case the closest examination failed to reveal 

even a rudimentary leg, and there was cer- 
tainly " no empty socket or other suggestion 
that the rest of the leg had been lost."' 

4. Specimen of Palinurus penicillatus with 
an -^ antenna-like flagellum growing up from 
the surface of the (left) eye." 

5. The female crayfish has normally a pair 
of oviducal openings on the bases of the ante- 
penultimate pair of walking legs. This .speci- 
men possessed in addition a pair also on the 

Fig. ;. Supernumerary wine on u- ^ 1 • ■ i ^ ^• 

, ^ ..^ ,^ ,/ *' ijenultmiate, showmg irregular segmentation, 
leftside. — After Bateson ^ . , . , . , 

6. Another specimen, also of the crayfish, 

possesses an extra pair of oviducal openings, as in the last, except that they 
were placed on the last pair of legs, skipping the penultimate. It is note- 
worthy that this is the normal position for the sexual organs of the male, 
except that the openings were placed in their own proper position on the leg 
and not " at the posterior surface of the joint as the male openings are." 

7. Bateson himself examined 5S6 female crayfish for abnormalities of 
oviducal openings. Of this number he found 563 were normal and 23 
abnormal, as follows : 

1. Extra oviducal opening on left penuUimate leg 7 

2. Extra oviducal opening on right penultimate leg .... 10 

3. Extra oviducal opening on both penultimate legs .... i 

4. Exti^a oviducal opening on both penultimate and last legs . i 

5. Single oviducal opening on left side only 3 

6. Single oviducal opening on right side only i 

Total abnormal specimens 23 

Bateson reports but one abnormal .specimen out of 714 males examined 
by him, and this abnormality consisted in the ab.sence of a generative open- 
ing on the right side. 

8. Among earthworms will be found many cases of imperfect segmenta- 
tion, showing more rings on one side than upon the other, often suggesting 
a spiral rather than a series of rings. Great irregularity is also found in the 
position of generative openings, as to whether paired or single, ^ although 
the male parts are always posterior to the female, whatever the number of 
the ring on which either is borne. 

Cervical fistulae and auricular appendages in mammals.^ 

Cervical fistulae are openings in the neck, occurring singly or in 
pairs and located anywhere from the median line backward as 

I Bateson, Materials, etc., pp. 156-166. - Ibid. p]). 1 74-1 So. 



MERISTIC VARIATION 



45 



far as the angle of the jaw. The opening is sometimes sHght, 
but often it extends completely to the pharynx. In the latter 
case it is possible to pass an instrument the size of a small 
quill, provided the opening is comparatively straight, otherwise 
its completeness or incompleteness may be ascertained by the 
injection of a licjuid. 

Bateson cjuotes Fisher^ as describing sixty-five persons with 
seventy-nine fistulae. Fourteen of these were bilateral (occurring 




Fig. 6. Child with supernumerary auricle on each side of the neck. 
Bateson, from Birkett 



After 



on both sides), and fifty-one were unilateral, of which thirty- 
three were on the right side. He adds, " There was evidence of 
heredity in twenty-one cases." 

Auricular appendages, often called supernumerary auricles, 
are not at all uncommon. They are non-functional growths 
occurring in the neighborhood of the ear but below it, and are 
generally accompanied by some deformity of that organ. They 
consist of little flaps of skin or, more commonly, of cartilaginous 
growths identical in texture with that of the normal external ear. 

^ Bateson, Materials, etc., p. 175. Obvious errors in figures prevent further 
quotations that would otherwise be of interest. 



46 VARIATION 

One of the most remarkable cases ever described is that of 
an infant brought to Guy's hospital in 185 1.^ Another was 
of a child having a well-developed supernumerary auricle on 
each side of the neck (see Fig. 6). These appendages were 
easily removed and proved to be entirely cutaneous, though 
each was served by a small artery. 

Whether cervical fistulse are to be regarded as remains of 
unclosed gill slits, or whether they are to be regarded as repeti- 
tions of the external ear, in any event their presence shows a 
pronounced tendency to repeat certain characteristic structures 
in this particular region of the body. 

Growths of this character are by no means confined to man. 
Cervical auricles (the so-called " wattles ") are common in sheep, 
especially merinos. They are well known in goats and are ex- 
ceedingly common in many strains of unimproved swine. Strange 
as it may seem, these repetitions of the ear appendages are un- 
known in either the horse or the ox. 

Meristic repetition in mammae.- One of the chief distinguish- 
ing features of mammals is milk secretion. Speaking generally, 
this occurs at some point or points on either side of the ventral 
surface of the body on lines running from the armpit to the 
groin. In swine and in dogs it is distributed throughout the 
entire extent of these mammary lines. In cattle, horses, goats, 
sheep, etc., it is confined to the rear extremity of the line, and 
in the elephant it is as decidedly forward, the udder being located 
at the armpit. In the human being the point of normal activity 
is relatively further back (down) than in the elephant, but yet 
above the middle. 

This latter point is established by the fact that supernumerary 
nipples are found both above and below the normal. The fact 
that no less than three supernumeraries have been found above 
indicates that the normal mamm?e are perhaps fourth in a full 
series. It is to be noted in this connection, however, that in 
most cases supernumeraries are situated below rather than above 
the normal. These structures vary all the way from mere nipples 
resembling warts and entirely unaccompanied by mammary tissue 

1 Bateson, Materials, etc., p. 178. ^ Ibid. pp. 1S1-195. 



MERISTIC VARIATION 47 

up to well-formed organs fully functional. Curiously enough super- 
numerary mammae are more common in men than in women. 

Bateson ^ quotes Bruce as having found in 2 3 1 1 females fourteen 
cases (0.605 percent), and in 1645 males forty-seven cases (2.857 
per cent). In another series 315 subjects were examined, show- 
ing twenty-four cases {^ .6 per cent), nineteen being male and 
five female. Bardeleben is also quoted as having examined 2736 
recruits (all males, of course). In this series "637 cases (23.3 
per cent) were seen, 219 being on the right side, 248 on the left, 
and 170 on both sides." 

The largest number of supernumerary mammas ever recorded 
was in a subject described by Neugebauer.^ This patient had 
five pairs of nipples, of which the fourth, numbered from above, 
was the normal. When the child was being suckled milk oozed 
from each of the uppermost pair, but all other supernumeraries 
yielded milk only with pressure. 

Extra teats in cows are too common to need mention except to 
call attention to their excessive number. The cow Rose, famous 
for her record at the Illinois Station,^ had in all eight mammae, 
six of which were fairly well developed, though only four were 
functional."^ It is noticeable that supernumeraries are nearly 
always posterior to the normal or else constitute a doubling of one 
of the normals. Every milker knows by sad experience that these 
supernumeraries are not only common but frequently functional. 

A close study of this subject shows that repetition of these 
parts may be by pairs or singly ; that the repeated parts may be 
on the same or on different levels ; that they may be out of line, 
being in some cases very near the median, and that the normal 
nipple may be doubled. From the latter fact we further establish 
the point that meristic variation may occur in two ways, — either 
by addition to the series or by division of a normal number. We 
shall find the same in teeth. 

1 Bateson, Materials, etc., pp. 182-183. 

2 Ibid. p. 183. 

^ See Bulletin A^o. 66. 

* These supernumeraries were not symmetrically placed. On the right side the 
two extra teats were placed behind the two functional, as is commonly the case ; 
but on the left side only one supernumerary was so placed, while the other was 
between the two functional teats. 



48 VARIATION 

Meristic variation in teeth. As Bateson remarks, "Teeth 
arise by special diilcrcntiation at points alon^ the jaw, as mammas 
arise by special differentiation at points along the mammary line," 
and we shall see that with teeth as with mamm?e these points 
of special differentiation may frequently lie outside the normal 
region, that they are subject to increase or decrease in number, 
and that the increase may be due either to the addition of a mem- 
ber to the series, to the interpolation of a member, or to the 
division of a normal member. 

Before considering special cases it is well to note that the 
similarity between the right and left jaws is that of ordinary 
bilateral symmetry, but that there is also a kind of symmetry, 
not very close but still marked, between the dentition of the 
upper and that of the lower jaw. It should be further noted 
that in many animals, as in the shark, alligator, etc., the denti- 
tion constitutes a series in which the separate teeth differ from 
one another mainly in size. But mammals for the most part are 
heterodont ; that is, the series is broken up into groups which 
differ among themselves, though the members of the separate 
groups resemble one another closely. Thus the incisors are 
quite different from the canines, which in turn differ from the 
premolars and the molars. The different incisors, however, 
are very much alike, and the same is true of the canines and the 
various molars and premolars. Meristic variation in a heteroge- 
nous series like this is manifestly much more complicated than 
in a simple series like the mammae or the ribs. With this intro- 
duction attention will be called to a few special examples quoted 
from the 237 cases that have been collected by Bateson. ^ 

1. One hundred and fifty-two adult skulls of anthropoid apes showed 
twelve cases of extra teeth. One was an incisor, one was anomalous, and the 
others were molars. This is nearly 8 per cent abnormal, as against 425 
Old World monkeys that showed but two cases of extra teeth, — less than 
one half of i per cent. 

2. Adult orang, with an additional posterior molar on both sides above 
and on the left side below. No trace of extra molar on right side was dis- 
covered, " though there is almost as much room for it as on the left side." 
Extra molars perfect but slightly smaller than the normal. 

^ Bateson, Materials, etc., pp. 105-273. 



MERISTIC VARIATION 



49 



3. Skull (orang) No. 2043^?, Oxford Museum, is normal except as to the 
second premolar in tlie upjjer jaw {/i'-). Both these teeth are missing from 
their proper place. There is plenty of space on the left side but somewhat 
less than the normal on the right side. The missing tooth of the right side 
is present in the skull, but instead of being in its proper place it stands up 
from the roof of the mouth within the arcade immediately in front of the 
right canine and almost exactly on the level of the second incisor, being in 
the premaxilla at some distance in front of the maxillary suture. 

Discussing this case, Bateson observes : 

That this tooth is actually the second premolar which has by some means 
been shifted into this position there can be no doubt whatever. It has the 
exact form of the second premolar and is of full size. It stands nearly verti- 
cally, but is a little inclined towards the outside. The canine is, by the 
growth of this tooth, slightly separated from the second incisor, and the first 
premolar is consequently pushed also somewhat further back. Hence it 
happens that the diastema space for the second premolar on the right side 
is not of full size. This should be understood, as it might otherwise be 
imagined that the contraction was due to a complementary increase in the 
size of the other teeth, of which there is no evidence. 

The missing premolar on the left side was not visible, but " on 
the left side of the palate there was a very slight elevation at a 
point homologous and symmetrical with that at which the second 
premolar on the right side was placed. ... A small piece of 
bone was here cut, away, with the result that a tooth of about the 
same size and formation as /^ was found imbedded in the bone." 
In this case, therefore, the upper premolars on both sides had 
" traveled away from their proper positions and taken up new 
and symmetrical positions in the palate, anterior to the canines." 

As Bateson pertinently remarks (italics and parenthesis mine), 
"The facts of this case go to show that the gc7'in of a tootJi con- 
tains ivithin itself all the clcuicnts necessary to its dei'clopnient in 
its oivn true form [even in an abnormal position], provided of 
course that nutrition is unrestricted." This is a significant point 
of peculiar interest to students of thremmatology, not because of 
its bearing upon dentition but because of the light it affords upon 
the basis of variability and the ultimate units of variation. 

4. Gorilla from the Congo, with a fifth incisor standing almost in the 
middle of the lower jaw. It has the characteristic chisel shape of the incisor, 
but it is " turned half round so that the plane of its chisel stands obliquely." 



50 



VARIATION 



5. Dog with lower jaw and teeth normal, but with upper canines imper- 
fectly divided. The division was more complete on the right side, forming 
practically two canines standing in line with the regular teeth. 

6. Dog with first premolar in right side of upper jaw doubled, both teeth 
being normal in shape, the anterior somewhat the larger. 




Fig. 7. Merism in teeth : canines partially divided. — After Bateson 

7. Dog with an extra premolar on both sides above and below, the denti- 
tion formula beinir t> ■ 

8. Sledge dog : " All teeth normal, e.xcept left upper / -. This tooth nor- 
mally has two roots. Here it is represented by two teeth, each having one 
root." 

9. Absence of first premolar frecjuently quite common in Eskimo dogs, 
suggesting a breed peculiarity. 

10. Among domestic dogs supernumerary molars were found in twenty- 
eight cases out of 345 skulls examined, as follows,^ the normal dentition of 
the dog as to molars being two above and three below (/// 2). 

m^ on both sides and «■* on one side i case 

n^ on both sides 2 cases 

m^ on one side 9 cases 

n^ and w7* on one side only 2 cases 

m'^ on both sides 6 cases 

;«* on one side only 8 cases 



This Strongly suggests the formula m |, which is that of 
Otocyon {Lalandes clog) and of the fossil Amphicyon, the sup- 
posed doglike progenitor of the bears. It calls to mind the 
further remarkable facts that Otocyon itself varies from m | 
to m I and that it is the only mammal outside the marsupials 



^ Bateson, Materials, etc., p. 220. 



MERISTIC VARIATION 5 1 

that ever has four molars on both jaws/ which goes far to indi- 
cate a marsupial ancestry. 

Remembering that the teeth are considered as one of the few 
most reliable bases for classification, the remarkable variation in 
their number, character, and position throws no little light on 
the manner in which variation behaves, which is the chief reason 
for their extended notice here. 

Supernumerary eyes. The development of extra eyes seems 
to be confined to insects, which afford a number of excellent 
examples of the development of normal tissue in abnormal 
situations. 

Bateson's Nos. 419 to 421 are all cases of the development 
of a third eye in Coleoptera. In every case these extra eyes are 
c}uite distinct from the normal. In No. 419 the supernumerary 
was small and lay abutting against but distinct from the right 
eye. Its color was brownish yellow, while the normal eye was 
black. In Nt). 420 the extra eye was on the left side but quite 
independent of the normal eyes, which were exactly alike. In 
No. 42 1 the extra eye was on the left side of the head, which 
was rather less developed than the right. This eye is borne 
upon an irregular chitinous loop, having a diameter of about 
2.5 mm. This loop is attached to the substance of the head 
before and behind, and these two attachments are distant from 
each other about i mm. The diameter of the eye is about 2.5 mm., 
thus occupying the full surface of the loop, and its faceting is 
said to be "not cjuite regular, and finer and slighter than that of 
the normal eye." It is thus a very good attempt at a functional 
third eye. 

Supernumerary wings in insects. Bateson ^ reports and de- 
scribes fifteen cases of extra wings among insects, — sometimes 
on one side, sometimes on the other, but generally if not always 
smaller than the normal ; sometimes plainly identified with the 
fore wing, more frequently with the posterior ; occasionally nor- 
mal in coloring and scaling, but as a rule abnormal. In one in- 
stance it took the form of a large upright scale and in another of 
a winglike appendage to the left anterior wing. 

1 Lydekker, Library of Natural History, p. 580. 

2 Bateson, Materials, etc., pp. 281-285. 



52 VARIATION 

Meristic variation in horns. ^ These appendages afford good 
material for studies in variation. They sometimes consist of 
horny matter (cattle, sheep, rhinoceros, etc.) and sometimes of 
true bone, as in the deer. They sometimes persist through life 
(cattle, sheep, goats, etc.) and sometimes are periodically shed, 
as with the antlers of the stag. They sometimes, as in cattle, 
have a bony case, which is a true outgrowth of the skull, but 
often, as in the rhinoceros, they have no connection whatever 
with the bone beneath. Again, the antlers, which are bony, sep- 
arate with a clean scar from the bone of the skull, as a leaf 
stem parts from its twig. 

The meristic variations of horns are no less remarkable than 
their substantive variations just mentioned. They are for the 
most part symmetrically placed in pairs on either side of the 
skull just above the eyes, though the horn of the rhinoceros is 
borne upon the nose and therefore upon the median line. 

Variation in number occurs cither symmetrically or asymmet- 
rically. If the rhinoceros has an e.xtra horn it will be just 
above and on the median line with the normal. Sheep may have 
an extra pair just external to (behind) the normal,^ or there may 
be three on one side and two on the other. In the latter case the 
third horn will be a little one lying between the normal and the 
more ordinary extra horn. In still other cases, according to 
Bateson, a double core will be found incased in a kind of 
"double-barreled " single horn. 

Among cattle no increase in the normal number of horns is 
known to the writer, but their entire absence is common. 
Indeed, the readiness with which the polled character appears is 
astonishing,^ particularly as it is associated with a peculiar prom- 
inence (the poll) lying between and often slightly below the 
normal base of the horns. In cattle, meristic variation in horns 
seems to be associated neither with divided horns or extra 
prongs. 

1 Bateson, Materials, etc., pp. 285-2S7. 

2 Four-horned breeds are not unknown. Bateson, Materials, etc., p. 2S5. 

3 It is a well-known fact that if either parent be polled the horns are almost 
certain to be absent in the offspring, and Storer, in his Wild White Cattle of 
Great Britain, says there is evidence that these park cattle have been several 
times alternately polled and horned since their inclosure in the parks. 



MERISTIC VARIATION 



53 



Besides sheep Bateson gives three specific cases of increase in 
the number of horns, as follows: (i) a family of goats in which 
the four-horned character was hereditary for " many genera- 
tions " ; (2) chamois with two " well-formed and sym- 
metrical extra horns " ; (3) roebuck, two specimens of 
which are figured. Of these one has two horns on one 




Fig. 8. Abnormal horns in roebuck : all but one have undergone meristic 
variation. — After Bateson 

side and three on the opposite side, while the other has three on 
one side, the other being normal, consisting of a single horn 
with one prong near the summit (see Fig. 8). 

Meristic variation in digits.^ Variations in these parts are 
peculiarly complex. There may be an increase or a decrease 
not only in the total number but also in the parts or joints that 
compose the several members. 

The best example covering both these points in the same 
individual is Bateson's No. 48 5. ^ In this case the right hand 

1 Bateson, Materials, etc., pp. 311-410. ^ Ibid. p. 327. 



54 



VARIATION 



has the usual number of digits, but the thumb has three instead 
of two phalanges, though its general shape is normal. In the 
left hand there is much confusion in the region of the thumb. 
There is an extra digit, but its true character is not so evident. 
It is sharp, like a finger, but functions as a thumb. Internal to 
this is a thumblike supernumerary with a true nail, but from 
its position it is functionless (see Fig. 9). 




Fig. 9. Meristic variation in the hand : right and left hands of the same indi- 
vidual, showing on the left hand a duplication of the forefinger at the 
expense of the thumb, and on the right hand an extra joint in the thumb. 
— After Bateson 

A fifth real finger, making six digits in all, is not uncom- 
mon. Its true position, however, is by no means always easy 
to determine. 

Speaking generally, extra digits may arise in three ways, — 
cither by addition to the series of an outside member next the 
thumb or the little finger, by the insertion of a member at some 
point within the series, or by the doubling of a member. Just 
which has taken place in any given case is not always easy to 
determine. 

Reduction in the number of digits is common and takes place 
in three ways, — by the loss of an outside member (generally 



MERISTIC VARIATION 



55 



the thumb, when the radius is absent), by the suppression of 
a member within the series (ectrodactyhsm), or by the union of 
two or more members (syndactylism). 

Syndactyhsm may occur in all degrees, from mere webbing 
to a real bony union, as in the case of solid-hoofed hogs. Fig. lo 

A B 




Fig. io. Degrees of syndactylism in digits: the general shape of the member is 
preserved even when one digit is suppressed. — After Bateson 



exhibits a case, Z>, in which the normal shape is preserved in 
the absence of a member (ectrodactylism), with nothing to sug- 
gest a union ; that is to say, digits iii and iv seem to be fully 
represented by a single digit, normal in character but replacing 
two members of the usual series. 



56 VARIATION 

To fully appreciate the significance of this subject we need 
to remind ourselves of evolutionary history with respect to digits. 

Man, for example, has normally five digits in all extremities. 
The same is true of the bat. The ox has only two toes and the 
horse but one, yet there are rudiments of others in both cases, 
strongly suggesting that at some remote period the number might 
have been greater. 

All things considered, it looks as if, for some unexplained and 
at present unexplainable reason, animal life in most of its higher 
forms had been originally constructed upon a plan of five as 
regards the extremities. True, many, if not most species, have 
long since departed more or less widely from the original plan, 
and yet the numeral five is as distinctly characteristic of the digits 
in animals as it is of petals in the rose family among plants. 

How this number has been gradually reduced to a final form, 
sometimes of two, as in cattle, sometimes of one, as in horses, 
is a chapter in development that belongs to the ancient history 
of evolution. Moreover it is a chapter that, for obvious reasons, 
must be read backwards and reconstructed from its fragments. 

It will assist in this reconstruction, and, what is of more 
consequence to the breeder, it will throw much light upon the 
manner of development and the unit of variability, if the stu- 
dent will consider the present condition and evident ancestry of 
a few characteristic species with respect to digits. 

Bats have five digits in both wing and leg, though the thumb 
is modified into a strong claw. 

Birds have three digits in the wing, namely, i, the thumb, 
which makes the so-called bastard wing; ii and iii, which make 
the true wing ; iv and v, missing. Radius and ulna are both 
present. In the leg the fibula is a mere splint, lying by the 
tibia. 

There is but one metatarsus, but it is large and heavy, ending 
in three pulley-like surfaces, over which play the tendons that are 
attached to the three toes directed forward (ii, iii, and iv). This 
plan suggests that the three middle metatarsals of the normal 
foot have here become united along the shank into one, but 
with three surfaces preserved for attachment of digits. Most 
birds have also a toe behind. This is regarded as digit i, but 



MERISTIC VARIATION 



57 



no bird has shown a trace of v. Added together, this all means 
that birds have lost digit v from the leg, if they ever possessed it, 
and IV and v from the wing, with i -in a fair way to ultimately 
disappear from both wing and leg, except when functional in the 
latter. 

The cat has normally four digits (ii to v) on each foot, all 
with three phalanges, and all furnished with claws. Besides this, 
I is represented on the fore foot by a pollex (thumb) of two 
phalanges, and a non-retractile claw, while on the hind foot the 
hallux (great toe) is rudimentary, consisting of a small bone 
articulating with the cuneiform but bearing no claw. Of all 
animals, aside from man, the cat is the most subject to supernu- 
merary digits, especially on the fore foot. In the great majority of 
cases the doubling is in the region of digit i. Often the extra mem- 
ber is shaped, not like its neighbors, but rather as if belonging 
to the opposite foot, though sometimes it is indifferent. For 
exhaustive material on this subject, see Bateson, Materials for the 
Study of Variation, pp. 313-324. 

Speaking generally, the dog tribe has five toes in front ^ (digit 
I not touching the ground) and four behind (i absent). 

The seal has five digits on all extremities, though the hand is 
modified into the flipper, and the foot is but slightly functional 
and evidently well on the road to extinction. 

The whale generally has five digits in front incased in skin 
to form a flipper, though this number is often reduced to four, 
and in all cases 11 and iii have more than the usual number of 
joints. The only traces of a hind limb are a few small bones 
beneath the sacral region and occasionally a part of a limb.^ 

In the manatee and the dugong the process has gone farther. 
Though these aquatic mammals have exceedingly serviceable 
flippers with five digits, yet the hind leg has been entirely lost. 
The vertebrae in the sacral region are not united, and even the 
pelvis is represented only by a pair of splint bones, though some 
fossil forms show a rudimentary femur or thigh bone.^ 

1 Excepting the African hunting dog, which has four (Lydekker, Library of 
Natural History, p. 496). 

2 This is similar to the loss of wings in the case of the New Zealand apteryx. 
^ Lydekker, Library of Natural History, p. 1156. 



58 VARIATION 

The bear has five toes, all round, with an additional claw in 
digit II behind, which he uses for combing. 

In mice and rats digit I'in front is rudimentary. This case is 
unique because in most instances, where a difference is notice- 
able, the reduction in digits has proceeded farther behind than 
before. 

Snakes, especially the large ones, occasionally show external 
vestiges of hind legs, and internally are frequently found traces 
not only of the pelvis but likewise of the thigh bone or femur. ^ 
This shows clearly that the snake is a somewhat recent form 
developed from lizard-like ancestors with limbs, the hind pair of 
which must have been placed not far from the middle point of 
the much-elongated body. This view is strengthened by the fact 
that as a rule but one lung is developed, showing that the body is 
more slender than formerly. 

Of all studies in digits the most interesting is that of the 
ungulates or hoofed animals. It is also the most profitable, 
because the majority of our valuable domesticated animals are 
included in this classification. 

The interest arises from the fact that out of this stock have 
developed two very different forms of feet, viz. the two-toed (as 
cattle) and the one-toed (as horses), both evidently having 
descended from five -toed ancestors, each by a process of its own. 

For example, cattle, sheep, deer, pigs, etc., have two. toes (iii 
and iv) well developed into a serviceable foot, with two others 
(ii and v) standing behind, not touching the ground (pigs), often 
rudimentary (deer), and frequently represented merely by splints 
(cattle). Occasionally all trace of these digits is lost (giraffe). 

On the other hand, the horse and his kind have but a single 
toe (hi) ; but on either side is a well-developed splint, the re- 
mains of the second and fourth metacarpals in front and of the 
corresponding metatarsals behind. They are, however, without 
functional significance, being attached only above and extend- 
ing downward with slender shafts and free ends not supplied 
with digits. 

In this connection it is to be noted that the extinct protohippus 
of the United States and the hipparion of Europe, both decidedly 

1 Lydekker, Library of Natural History, p. 2535. 



MERISTIC VARIATION 59 

horselike animals and regarded as ancestors of the modern horse, 
had each three toes that probably reached very near the ground. 

Passing still further back (down) in geologic time and looking 
for a still more remote ancestor, we get beyond what can be 
called a true horse, as can the protohippus and the hipparion. 
But yet there is among these long-extinct forms sufficient horse- 
like character to suggest ancestry, as with the forest horse and 
desert horse of the Whitney find in Wyoming, forty inches high 
and three toes down.^ As we progress in this direction, however, 
the toes increase in number to four and even five, clearly indi- 
cating that the modern horse has developed from a five-toed ances- 
tor like the Eohippus, twelve to sixteen inches high and all toes 
down, also discovered in Wyoming where it flourished, according 
to Osborn, some three million years ago or thereabouts.^ 

If we begin with the modern two-toed species and attempt to 
read their story backwards, we soon land among the same four- 
or five-toed primitive forms just mentioned, forcing the conclu- 
sion that the one-toed and the two-toed species of recent times 
have each descended from five-toed progenitors, — indeed, we may 
even believe from the same five-toed progenitors. 

The manner of this descent is not difficult to trace by the 
comparison of modern species with similar extinct forms in suc- 
cessive downward (backward) geologic times. In almost the 
lowest tertiary rocks of both North America and Europe occur 
fossil remains of large ungulates. These '* Coryphodons " were 
supplied with five-toed feet much like the elephant of to-day, 
that has survived by virtue of his teeth and in spite of his feet. 

Ascending to the Miocene Tertiary, we find large ungulates 
still remaining, but digit i is gone, while the metacarpal (or meta- 
tarsal) has become much lengthened and the third and fourth 
members greatly strengthened, not only in their own development 

1 Henry F. Osborn, Origin and History of the Horse. 

2 The development of the horse from an ancestor only twelve to sixteen inches 
high and with five toes, all down, is the best instance of progressive evolution 
of which we have any knowledge. Doubtless the evolution of other species has 
been no less extended and fascinating, but of no other case do we possess so 
complete a history, thanks for which are in large measure due to the generosity 
of the late William C. Whitney and to the labors of Professor Henry F. Osborn. 
See also chap, x, sect. ii. 



6o VARIATION 

but also as regards their articulation with the small bones above. 
This foot is now on the road to becoming indifferently either a 
two-toed or a one-toed form, depending upon whether ii and v 
reduce together or whether iii takes the lead. 

In this connection certain intermediate or stranded forms are 
of no little interest. For example, the elephant has five toes in 
front, with four and sometimes three behind. The rhinoceros has 
three both before and behind, but the extinct form often had 
four. The tapir, which is also regarded as a remnant of ancient 
life preserved until the present, has generally three toes, though 
sometimes four and occasionally two. In any case, however, digit 
III is largest and symmetrical in itself, showing affinity with the 
line of descent that has developed the single-toed forms. 

The camel has two toes, while the nearly related chevrotain 
has four, two being reduced. The hippopotamus has four short 
toes, all down, all hoofed and partly webbed, showing affinity 
with two-toed forms in that the symmetry is about a line drawn 
between digits iii and iv. This is the same plan as that of the 
pig, except that in the latter the foot is more contracted, the 
toes being flattened on the inside and the second pair not touch- 
ing the ground. 

The kangaroo is anomalous, having five toes in front and in 
general four behind, of which iv is much the largest ; v is small, 
and II and in are much reduced and incased in a common 
integument. 

With this brief survey of specific differences in respect to 
digits, certain individual deviations will have an added meaning. 
Bateson gives us the following : ^ 

1. Horse having supernumerary toe on inside of right fore foot, presum- 
ably digit II. It articulated with an extra bone in the lower row of the 
carpus and was provided with a hoof, " convex both sides, resembling the 
hoof of an ass" (see Fig. i i). 

2. Foal having two toes on each fore foot, otherwise normal. The car- 
pus was in this case normal, but the extra toes were again borne on the 
inside and were provided with a small hoof. 

3. Horse having a rudimentary digit on inside of left hind foot. This 
again results from a slight development of digit 11, which is the most com- 
mon cause of polydactylism among horses. 

1 For variation in the feet of the horse, see Bateson, Materials, etc., pp. 360-372. 



MERISTIC VARIATION 



6l 



More rare than this are: (i) the development of iv, making an extra 
toe on the outside ; (2) development of 11 and iv, with iii normal, making 
three toes in all, after the fashion of the protohippus ; and (3) development 
of II and IV vf'ith iii aborted, resulting in an abnormal two-toed foot. All 
these forms are well known among horses. 

4. Horse with supernumerary on outside of each fore foot, illustrating 
condition mentioned above (development of digit iv) (see Fig. 12). 

5. Horse with both splint bones 
bearing digits on each foot, illustrat- 
ing condition 2 (11 and iv developed 
normal, making a three-toed horse). 




Fig. II. Right fore foot of horse (front 
view) : as the hoof of the horse is re- 
garded as digit III, this extra member 
is to be considered as digit 11. — After 
Bateson 




Fig. 12. Right fore foot of horse 
(rear view) : this extra toe is to 
be regarded not as digit 11 but 
as digit IV. — After Bateson 



62 



VARIATION 



6. Foal with right fore foot bearing two complete digits symmetrically 
developed, each bearing well-formed hoofs'that are flattened on the inner 
sides and curve toward each other like those of the artiodactyles (cattle, 
etc.). This illustrates condition (3) 
just mentioned (see Fig. 13). 

Cattle, sheep, and pigs af- 
ford deviations no less inter- 
esting : ^ 




Fig. 13. Foot of horse: digit iii sup- 
pressed, digits 11 and IV developed. — 
After Bateson 



I. Calf having three digits on 
right fore foot, borne on a single 

common bone after the fashion of the birds and fully 
symmetrical (see Fig. 14). 

2. Heifer having three fully developed toes on 
each hind limb. In this case the supernumerary was 
clearly digit il. 

3. Calf with "supernumerary toe placed between 
the digits of the right manus (fore foot). This toe 

had a hoof and seemed ex- 
ternally to be perfect, but on 
dissection it was found to 
contain no os.sification, but 
was entirely composed of 
tibrous tissue and fat." 2 

4. Cow, full-grown, right 
fore foot with four digits 
arranged in two groups of 
two each (see Fig. 15). 

This is clearly a case in 
which the increase is due, 
not to the reappearance of 
an ancient lost toe like il or 
V, but rather to the doubling 
of the nortnal digits III and 
IV through ordinary ineristic 
variation?^ 

5. Calf, left hind foot 
with five toes, " an inner 

Fig. 14. Right fore foot of calf: three digits group of two toes curving 
present, each supplied with both flexor and toward each other and an 

outer group of three, of 





extensor tendons. — After Bateson 



1 Bateson, Materials, etc., pp. 373-390. - Ibid. p. 377. 

3 No case is better than this to suggest caution to the student of evolution. 
When an extra toe appears among those forms whose ancestors were known to 



MERISTIC VARIATION 



63 



which the middle one was ahiiost bihiterally symmetrica], while the hoofs 
of the other two turned toward it." ^ 

Bateson says of the pig that he knows of no case of polydac- 
tylism in the hind feet. All cases described are of the fore feet, 
and the extra toes are on the internal side 
of the digital series. 

Syndactylism in cattle, sheep, and pigs. 
By this term is meant a real union of 
digits II and iii into a single bone incased 
in a single hoof, as in the solid-hoofed hogs. 

According to Rosenberg, as quoted by 
Bateson,^ in the normal sheep " the meta- 
carpals II and V are distinct in the 
embryonic state, afterwards completely 
uniting (fusing) with iii and iv." "^ This 
throws some light upon the whole ques- 
tion, as tending to explain not only certain 
cases of polydactylism but all cases of 
syndactylism.* Again quoting Bateson : 




Fig. 1 5. Said to be the right 
fore foot of cow : digits in 
two groups of two each. 
— After Bateson (from 
Delplanque) 



1. A young ox having the two digits of the 
right fore foot completely united. 

2. Calf: each foot having only one hoof, 
though all the bones were normal. 

3. Same as above, except that in the fore foot the normal digits (iii and 
IV) were completely united, bearing a single hoof. The same condition 
was found behind, except that the hoof was more pointed. 

4. A fore foot and a hind foot of the same individual (pig), in which 
the two chief digits were completely united, viz. represented by a single 
series of bones. 



possess a greater number of digits, it is habitual with many to regard it as a case 
of atavism, — the reappearance of a long-lost character. But how is it in the case 
of man when a si.xth or even seventh digit appears ? This must be meristic varia- 
tion and not atavism, because no six-toed species of any sort has ever been 
described or its existence suspected. Meristic variation, therefore, is not limited 
to lost characters or to numbers once normal, but may go far in excess of either. 
Here, then, is need for discrimination, for even the appearance of a character that 
has been once lost is not absolute evidence of atavism. 

1 Bateson, Materials, etc. p. 381. - Ibid. p. 3S3. 

3 The former from failing ever to unite, the latter from a continuation of the 
fusing process to include in and iv. 

* That is, II unites with iii, and v unites with iv during development. 



64 



VARIATION 



Other and similar cases are given, though the latter is the 
only one described in which the syndactylism is complete in all 
four feet. It is, however, generally simultaneous in fore and 
hind feet.^ 

Absence of parts in a linear series. Men with hands but no 
arms, with feet but no legs, are not unknown. Whether the 
missing parts are really dropped out of the series, or whether 

they were originally present but 
suffered abortion during embry- 
onic development, being repre- 
sented at maturity by rudimentary 
parts, is uncertain, though zoolo- 
gists would incline strongly to the 
latter view. The exact fact would 
have an important bearing upon 
the unit of variability, the nature 
of heredity, and the manner of 
differentiation. 

Whatever the fact in this re- 
gard, variations of this order are 
manifestly rare as compared with 
the increase or decrease in strictly 
multiple parts. In other words, 
while considerable deviation in the 
number of similar members (as 
fingers) is common, it is exceed- 
ingly uncommon for an entire 
group (as the hand) to be omitted, — rarely from the end of 
the series (as the foot or hand) and still more rarely, if ever, 
from the middle of the series, as would be the case in a truly 
missing arm (humerus, radius, and ulna), but with the hand 
present, coming directly from the body. 

Extra legs. The repetition of a member as complicated as a 
leg is extremely unusual but by no means unknown. The writer 

1 Bateson gives many similar cases, each with some peculiarity of its own. 
Solid-hoofed pigs are seen so frequently and at points so widely removed both 
in time and space (mentioned by Aristotle and reported from many regions of the 
earth) (see Bateson, Materials, etc., p. 3S7) that this would seem to be a variation 
that has often arisen afresh. 




Fig. 16. Meristic repetition in leg: 
right leg of beetle repeated in 
triplicate. — After Bateson 



MERISTIC VARIATION 65 

saw one specimen of a leglike appendage growing from the left 
side of the neck of a calf near the point of the shoulder. The 
leg was not more than two thirds the usual length, and was 
twisted and functionless, though it terminated with a hooflike 
growth.^ 

Extra legs are common in insects, sometimes throughout their 
entire length, sometimes doubling at the femur (see Fig. 16). 



SECTION III — MERISTIC VARIATION AND BILATERAL 

SYMMETRY 

Meristic variation among paired organs and those standing 
singly on the median line throws no little light upon the nature 
of bilateral symmetry and also incidentally upon the manner of 
variation. 

Speaking generally, paired organs may double on either side 
separately or on both sides (digits, legs, wings, etc.), or they may 
unite into a single organ with its axis on the median line (horse- 
shoe kidney). 

Most of the examples of meristic variation already given are 
of repetition in paired organs in bilateral symmetry. It remains 
to call attention to the opposite condition, — the fusion of a pair 
into a single organ standing on the median line : 

1. A good example of this is that of a roebuck having the horns com- 
pounded for full}' half their length into a single " beam " standing on the 
middle line "^ (see Fig. 17). 

2. A honeybee '"^ having the two compound eyes united into one at the top 
of the head with no groove or line of division between them.^ 

3. Posterior ends of kidney united (in man), forming a horseshoe kidney 
with three renal arteries on each side. This case is in sharp contrast to 
Bateson's No. 407, with a single large kidney on the left and two smaller, 
one below the other, on the right. 

1 Thi.s .specimen is de.scribed from memory, as it was seen before these phe- 
nomena were matters of personal interest. 

2 Bateson, Materials, etc., p. 460. 
^ Ibid. p. 461. 

* The compounding of eyes has already been mentioned. It apparently occurs 
only in insects, but is a good example of the development of highly differentiated 
tissue in abnormal situations, illustrating not only meristic variation but functional 
variation as well. 



66 



VARIATION 



Conversely, unpaired organs standing on the median line may 

be divided so as to form a pair of organs symmetrically placed. 
It should be noted that in general a single organ standing on 

the median line, as the nose, is symmetrical both with reference 

to itself and to the median line, but 
that for the most part paired organs, 
though symmetrical with reference to 
the median line, are 7iot tJicinselves 
necessarily synivietrical bodies (ears, 
arms, hands). In other cases of paired 
organs, however (eyes, kidneys), the 
members do have a kind of symmetry 
of their own. 

Again, nothing is more common, 
especially among plants, than to find 
a single organ on the median line 
appearing as a paired organ in cer- 
tain individuals or in nearly related 
species or varieties. 

Bateson gives as examples of the 
last the posterior petal in Veronica^ 
which in most related species appears 

Fig. 17. Compounding of paired ^g ^ pair of petals lying on either side 

organs: the two horns of this ^ , • i n i- 

roebuck are united into a single ^f the middle Ime. 

beam for a considerable dis- After giving numerous instances of 
tance, but afterwards they sap- division of median Organs in fishes 

arate. — After Bateson ... , . , . ^ 

and m msects, he cites authority tor 
saying that " The organs most often divided in man are the 
sternum, neural arches, uterus, penis, etc., and of these, speci- 
mens may be seen in any pathological museum.^ Organs more 
rarely divided are the tongue, epiglottis, uvula, and central neural 
canal." ^ These latter are in reality cases of a.xial duplicity.^ 




1 Bateson, Materials, etc., pp. 450-458. 

2 Teratology is that branch of biology which treats of abnormalities, and it 
affords many cases of e.xtreme variations. This study has been considered as 
curious rather than profitable, and yet, as such abnormalities are coming to be 
regarded as frequently due to a defective germ, it may yet prove that attention to 
cases of this order may furnish the key to the solution of questions involving the 
unit of variability. ^ Bateson, Materials, etc., pp. 559-566. 





Fig. i8. Double-headed turtle compared with the usual spechnens two to three 
days old. Note effect on shell plates. In this specimen the movements of 
the legs on opposite sides were not well coordinated. — After Bateson 



67 



68 VARIATION 

Fig. 1 8 shows a case of double head in the turtle. Many 
similar instances have been described, but this is especially inter- 
esting because " the two heads seemed to act independently, and 
it is said there was no concerted action between the feet of the 
two sides." The same phenomena of double monsters are said 
to be frequently noted in fish-hatching establishments. Among 
snakes " some twenty cases are recorded of complete or partial 
duplicity, nearly always of the head. Several of these were ani- 
mals of good size, and must have led an independent existence 
for some considerable time." ^ 

Similar cases of doubling are known in birds and even in mam- 
mals, but among these higher animals the practical difficulties 
in sustaining existence with extreme abnormality are very great, 
and they commonly do not long survive. 

Between this division of a single organ lying on the median 
line and the doubling of so important a part as the head, there 
seems to be no clear line of demarcation. This doubling may 
even go further, as in the case of the Siamese twins, until the 
specimen is regarded as essentially two individuals united by 
some sort of attachment. 

SECTION IV — SYMMETRY IN VARIABLE PARTS 

Without a doubt meristic variation in one organ of the body 
is likely, but not certain, to be accompanied by abnormality in 
another. For example, a variation among the digits of the fore 
foot is likely to be associated with a similar variation behind, still 
more likely on the opposite side, but not positively with either. 

Again, there is some suggestion of symmetry within the part 
itself in which the variation occurs. A good example of this is 
Bateson's No. 495 (Fig. 19). 

This is a left hand, and the four extra fingers seem to repre- 
sent not the thumb of that hand but the fingers of the opposite 
(right) hand, thus seeming to aim at a kind of secondary sym- 
metry within the member.^ 

In the description of this case we are told that this double 
hand and arm were very muscular, so that it was not possible 

^ Bateson, Materials, etc., p. 561. " Ibid. p. 335. 



MERISTIC VARIATION 



69 



to decide in the living subject whether or not there was a 
doubhng- of the bones of the forearm. The eight fingers were in 
two groups of four each, with a wide space between. The two 
" hands " were thus opposed to each other and could be folded 
upon each other. The power of independent action of these 
digits was limited, showing an insufihcient supply of muscles. If 
the two index fingers, iv and v (really ii and 11), were extended, 
the other six could be flexed ; either group of four could be 
flexed independently of the other, or the three fingers of either 




Fig. 19. Symmetry within the variable part. Here it would seem that an attempt 
has been made to repeat the hand, or rather that an attempt at repetition of 
the thumb has resulted in a doubling of the hand. — After Bateson 

hand could be flexed alone. The index fingers alone could not 
be flexed while the other six were extended. 

Bateson gives several other cases of "double hand" (Nos. 
496—500), all giving the impression that the doubling is not 
simply of digits but of a JuDid as a wJiolc. His No. 513 is the 
case of a double thumb, in which the two are symmetrically 
opposed to each other. 

It is unfortunate for our purpose that so large a proportion of 
cases cited as examples of mcristic variation should be among 
human subjects. This is only because it is here that the matter 
has been most studied. The idea has been advanced that domes- 
ticated species are more variable than wild ones, and man more 
variable than his simian congeners. The point is not well taken, 
because careful study shows the ape, the chimpanzee, the baboon, 
and the gorilla to present the same meristic deviations in respect 
to diijits and the same abnormalities in dentition as are found 



70 VARIATION 

in man. Again, while digital variation is exceedingly common 
in chickens, it is rare in birds generally, and is almost unknown 
in ducks and geese which have long been domesticated. 

The fallacy above alluded to seems to have arisen from the 
fact that domesticated species are better known than wild ones, 
and that certain variations at least are more likely to be preserved. 
In any event they are more strongly impressed upon our atten- 
tion. The truth seems to be that variability depends upon the 
nature of the part and the relative stability of the species in ques- 
tion, not upon its domestication or its place in the scale of life. 

We can therefore avail ourselves of any material bearing upon 
the general question wherever it may be found, hoping, however, 
for the early coming of the time when the variations within the 
particular field of thremmatology shall be better known and more 
accurately described. 

Asymmetrical development in symmetrical parts. The case of 
the narwhal illustrates a fact in xariation which, though seldom 
so apparent, is doubtless often potentially present, and if so, is 
certainly to be reckoned with by the breeder. 

In the narwhal the canine tooth (in the male only) develops 
as a tusk, often attaining a length of seven or eight feet, or half 
the length of the body. The peculiarity is that normally only 
the left tusk develops, and in the few cases seen in which both 
are developed the right tusk is spirally twisted from left to right, 
exactly like the left tusk, and not in the opposite direction, as 
we should expect. What is still more astonishing is that no case 
has ever been described in which the right tusk was developed 
alone instead of the left. Either both are developed or the 
left one only, and in the former case they are essentially both 
left tusks. 



SECTION V — MERISTIC VARIATION IN RADIAL SERIES 

Except in the lower forms, radial series are characteristic of 
plant rather than of animal life. In the branching of stems and 
the parts of flowers, members of radial series are everywhere 
about us. Their variations are always interesting (doubling of 
flowers) and often exceedingly valuable (stooling of grain). 



MERISTIC VARIATION 7 1 

Botanists would say that what seem to us as radial series, 
with the members standing on the same horizontal level, are in 
most cases really shortened stems, bringing these parts into a 
relation which is apparent rather than actual, as would happen if 
we could telescope any long stem until the leaves, regularly dis- 
posed along its length, should come to occupy the same plane. ^ 

In this view of the case the petals of flowers and the branch- 
ing of stems, as in the stooling of grain, would be examples of 
linear series very much shortened rather than of radial series, 
according to the strictest definition of the term. For our purposes, 
however, this structural point may be waived, and all apparent 
cases of radial symmetry treated as actual. 

Observations indicate and experiments show that members of 
such series may be increased in number almost indefinitely. All 
the members may be doubled simultaneously (as five petals 
increased to ten), or any one member (original segment) may 
double or even triple, or it may be entirely suppressed without 
reference to other members of the series. 

The natural method of doubling seems to be for cell division 
to proceed one step beyond the normal, gi^'ing rise to two instead 
of one. If this occurs in all the members (petals), then the 
members will all be doubled, as ten instead of five ; if only in 
part, then only that portion will be affected, making six, seven, 
or even eight instead of five. Thus we have clover running all 
the way from the normal three up to as high as seven leaflets. 

Manifestly if cell division proceeds two stages beyond the 
normal, each of the twin pair again dividing, it will result in 

1 Leaves are arranged in regular order upon the stems of plants according to 
a system constituting the mathematical series, J, |, |, |, etc., in which the 
numerator indicates the number of circuits around the stem to reach a leaf 
directly over the one with which the count was started, and the denominator the 
number of leaves that would be passed in such a circuit. It therefore repre- 
sents the number of members in a whorl of a shortened stem of this character. 

Corn, for example, belongs, with all other members of the grass family, to 
the fraction ^ , — built upon the plan of two. This number runs throughout the 
plant, and while the number of rows of corn on the cob may vary freely from 
eight to twenty-four, 710 case of an odd mimber of roivs //as ever been reported. 
This fact tends to set some limits to even so wayward a thing as meristic varia- 
tion, which seems never to have produced an ear of corn with an odd number of 
rows. This seems marvelous when we consider the havoc it works with digits 
and with even so complicated a structure as a head. 



72 VARIATION 

quadrupling that member of the series. If, however, only one of 
this pair should divide again, we should then have one plus two, 
or three, new parts in place of the one that was normal. Again, 
if all four should start and one abort, it would likewise result 
in three developed members instead of four that should have 
appeared. 

All these various processes may take place, but whatever the 
final result, and whatever number ultimately develops, the method 
is that of doubling through cell division, giving rise naturally to 
even numbers. Odd numbers are explainable, however, by sup- 
posing that one of a pair continues the process one step farther 
than its twin, or else that one of the members fails to develop. 
In these ways an original member of a radial series may at any 
time develop into two, three, four, or more ; and if all the mem- 
bers take part, a true doubling results. 

Meristic variation and cell division. In the last analysis, there- 
fore, variation in the number of members in a radial series is 
reducible to questions of cell division. Indeed, we may go further 
and note that all cases of meristic deviation arise in this manner ; 
that the preservation of the normal number of multiple parts 
depends upon successful cell division up to a certain (normal) 
point and its abrupt cessation at that point ; and that all sorts of 
abnormalities may arise through excessive multiplication, through 
abortion, or through some other disturbance of the process of 
cell division. 

This view of the case helps to explain why it is that meristic 
variations in radial series are among the easiest to explain of all 
variations which may present themselves to the breeder. 

Considerations of this character make clear the futility and 
shortsightedness of appealing to reversion or atavism to explain 
what may be a mere incident in cell division, — an incident, more- 
over, that may never have occurred in phylogeny, may not be 
even common in ontogeny, and is therefore not to unduly im- 
press the observer.! 

1 These terms will be frequently used in the text. Phylogeny refers to the 
development of the species, ontogeny to the development of the individual. 
The latter is supposed in a general way to repeat the steps of the former, though 
with this view of the matter important gaps are of frequent occurrence. 



MERISTIC VARIATION 73 

SECTION VI — IMPORTANCE OF MERISTIC VARIATION 

Nothing is of more direct benefit to man than the stooHng of 
grain, and the doubhng of flowers is of prime importance to 
students of the beautiful. Digital variation, and indeed most of 
the examples among animals, are not only of no practical use but 
they constitute deformities that would at once be eliminated from 
the fields of any intelHgent stockman. 

Their study is, however, useful to the student in two ways : 
first, as showing him that freaks are by no means uncommon 
and therefore not to be specially prized ; and second, to show 
the manner in which variation operates and the size of the unit 
involved, together with something of its relations to other and 
similar units in the same body. The careful student will not, 
therefore, waste his time in trying to establish a race of solid- 
hoofed hogs the first time a specimen of the kind turns up in 
his yard, but he will utihze the information afforded in meristic 
variation generally to advance his understanding of the manner 
in which variation behaves and of the relations that obtain between 
the several parts of a highly differentiated body. 

The purpose at this time is to secure a mass of characteristic 
facts on which future studies may be based. Most of the dangers 
of erroneous procedure in this field arise from a paucity of well- 
authenticated instances and from restricted views of their real 
significance. 

Summary. Meristic variation refers to deviations in the plan 
or pattern on which the organism is built. Its central thought is 
symmetry. Symmetry may be radial with the members identical, 
or it may be bilateral with opposite members, as optical images 
the one of the other. Distinctions of right and left arise from 
those of dorsal and ventral, and have reference to the relation of 
the individual to the outside world. Organs symmetrically placed 
may or may not have a symmetry of their own, but the ten- 
dency is for a part to establish some kind of symmetry within 
its own members. 

When parts are multiplied they may be like the other mem- 
bers of the series in which they arise, or they may imitate those 
of neighboring series (homoeosis). Repeated parts are especially 



74 



VARIATION 



subject to meristic variation. The general plan is preserved, but 
wide variation in the details is common, as in the nerve branches 
from the spinal column. 

The part repeated may be simple, like a digit ; or it may be 
an entire group, as a whole hand or an entire leg. 

Meristic variation has its seat in cell division. It is of little 
utility in animals though highly useful in plants, but its phe- 
nomena are valuable for the insight they afford into the man- 
ner of variation, the general persistence of plan, and the unit of 
variability. 

Exercises. Let the student give ten separate examples of 
meristic variation not mentioned in the text and describe each 
fully, stating all that is involved of symmetry, homoeosis, etc. 

ADDITIONAL REFERENCES 

Variation. A cock with no spurs on the leg, but with well-developed ones 

on either side of the comb. By E. S. Dexter. Science, VII, 136. 
Vegetable Teratology. By Maxwell T. Masters. 



CHAPTER V 

FUNCTIONAL VARIATION 

By functional variation is meant a deviation, not in form or in 
the number of parts but in the functions that they perform. The 
Hving animal (or plant) not only is something, but it does some- 
thing, and plants and animals differ among themselves not only 
in what they at-c but in what they do. 

Each portion of a highly differentiated organism has its own 
peculiar activity, which is essentially different from that of any 
other part of the same organism. These activities are not con- 
stant but variable ; and inasmuch as many animals and not a 
few plants are kept not for their appearance but for what they 
can do, any deviations in their performance ability are of prime 
importance to the breeder, who is bent upon their increased 
efficiency and their permanent improvement for the service 
of man. 

Now plants and animals are considered as high or low in their 
development according to the degree of differentiation or division 
of labor between their different parts. In the protozoon the func- 
tions of life are few, and its relations to the environment are 
simple. Accordingly its activities are exerted and its obligations 
to life discharged by the common mass of undifferentiated pro- 
toplasm, perhaps without so much as a stomach, reproduction 
being effected by a direct division of the whole mass. 

In higher organisms (metazoans), however, life is more complex 
and the responsibilities of existence are heavier. These are met 
by specialized structures, such as the mouth to take food, the 
stomach and intestines to dissolve and prepare it for use, the 
liver to convert certain portions into specially usable form, 
the lungs to absorb air, the blood vessels to carry it and the 
digested food to all parts of the body, where each extracts what 
it needs and can use. 

75 



76 VARIATION 

Then there are organs, as the kidneys, whose function is to 
remove waste products that would otherwise accumulate and 
destroy the body. There are others, as the udder and various 
glands, whose function is to manufacture some particular product 
to be used either within or without the body. There is a system 
(the muscular) for moving the body as a whole or for the exercise 
of any of its parts, and a network of nerves forming a ready and 
rapid means of communication. There is a heart to drive the 
blood, and perhaps a bony skeleton to hold the complicated mass 
together. 

Now the activities or functions of these various parts are by 
no means constant and invariable from day to day. In other 
words, there is probably as much deviation in function as in 
form, and for the purpose of the farmer it is even more 
important. 

Evolution not a study in morphology only. The mistake is 
often made of defining evolution as exclusively a study in mor- 
phology.^ It means more than that. Living beings are some- 
thing besides form, and their evolution something more than the 
development of their form ; indeed, in their service to man both 
animals and plants are valued less for their structure than for 
their function, which is what they can do. And so it is that 

1 " The problem of development is an acknowledged morphological problem." 
— C. B. Davenport, E.xperimental Morphology, Part I, Preface. 

The conception here alluded to is not difiicult to account for. The idea of 
evolution or development as opposed to the older assumption of special crea- 
tion was first announced at the very close of the eighteenth century, but was not 
generally before the public until the appearance of the Origin of Species, after the 
middle of the nineteenth century (1S59). At that time biologists were chiefly con- 
cerned in classification as based upon external structure or form. It is not strange, 
therefore, that the discussion should have first arisen, and the battles incident to a 
new, startling, and, in the popular mind, sacrilegious theory have been first fought 
out, in the field of morphology. 

Gradually, how^ever, biologists began to concern themselves more and more 
with internal structure (histology), and, quite to their surprise, they found them- 
selves still within the field of evolution. Then came studies in function (physi- 
ology), showing conclusively that this, too, is a matter of development and subject 
to variation and heredity. It is therefore not only erroneous but for the breeder 
dangerously misleading to consider the study of evolution as confined to the field 
of morphology, which is not the exclusive nor to him even the primary manifesta- 
tion of the great principle of evolution. There is evoluion of function as well as 
evolution of form. 



FUNCTIONAL VARIATION 77 

the breeder, intent upon enhancing their service to man, sees 
in the variation of the functions natural to domesticated animals 
and plants the greatest opportunity for improvement. 

So true is all this that the successful breeder may be distin- 
guished from the novice at this point. The latter is likely to be 
attracted, first of all, by form or color, because differences of this 
sort are striking and easily noticed ; while the former will always 
keep foremost in mind the question. Why is this animal (or plant) 
valuable to man, and what is it to do ? 

The student cannot, therefore, know too much about the 
natural functions of domesticated animals and plants and the 
deviations to which they are subject. He should know this, not 
only as a guide to his selection but also as constituting valuable 
information upon the nature of evolution and the possibility of 
influencing the causes that control the development of living 
beings, functionally as well as structurally. 

Instances of variation in functional activity are easily divisible 
into four classes. 

1. Variation in the degree of activity of normal functions 
between different individuals of the same species. 

2. Variations in the degree of activity of normal functions 
within the same individual. 

3. Modification of normal functions by external or other 
influences. 

4. Normal functions exercised under abnormal conditions. 

SECTION I — VARIATION IN THE DEGREE OF ACTIVITY 

OF NORMAL FUNCTIONS BETWEEN DIFFERENT 

INDIVIDUALS OF THE SAME SPECIES 

Variation in milk secretion. This is a function peculiar to one 
class of animals (mammals). It is the product of a highly spe- 
cialized structure and is practically confined to the female sex. 
Moreover, it is of peculiar economic as well as physiological im- 
portance, and there is no better example to bring out much that 
is involved in functional variation. 

The structure of mammary-gland tissue is characteristic 
wherever found, but the quality and flavor of its product (milk) 



^^ VARIATION 

are not the same for any two species (functional variation between 
species). 

Again, no two individuals of the same species can be depended 
upon to give exactly the same quality of milk, for herd records 
show that the milk of different cows varies naturally from less 
than 3 per cent to more than 6 per cent fat ^ (functional varia- 
tion between individuals). Nor is this dependent upon the food 
supply, for all authorities agree that the proportion of fat to 
other solids is dependent upon the individual and not upon her 
feed. Moreover, differences nearly as wide as these quoted may 
be found within the limits of a single herd and therefore under 
identical conditions as to feed. 

Still again, two individuals of the same breed will produce 
radically different amounts of milk or fat, whichever is measured, 
from identical amounts of the same kind of feed. This has been 
repeatedly and conclusively shown by Professor Fraser of the 
University of Illinois.^ Probably no fact in animal physiology is 
of more far-reaching importance than is this marked instance of 
functional difference between individuals. 

Three experiments were conducted in the attempt to deter- 
mine the limits of this difference between cows considered good 
enough for a place in a commercial herd. In the first ^ Eva 
produced 48 per cent more milk and 1 1 per cent more butter 
in ninety-one days than did Janet, and in doing so consumed no 
more grain and but y.G per cent more roughness. These cows 
were both mature, were fresh on the same day, and neither suf- 
fered accident during the experiment, yet Eva produced 1057 
pounds of milk and 12 pounds of fat out of an extra feed of 
112 pounds of hay and corn stover, — a difference greater than 
any margin of profit the dairyman may hope to realize. 

The second experiment was a comparison between Rose, a 
native cow nine years old, and Nora, a native cow six years old.* 

^ The actual range in milk is far greater than these figures. Single milkings 
have been known to run as low as 1.8 per cent fat, and Jersey cows near the close 
of lactation often give milk with 9.0 per cent fat. 

2 See Bulletin No. ji and Bitlletin A'o. 66, Agricultural Experiment Station, 
University of Illinois, May, 1898. 

3 Ibid. (51) p. 103. 

* Bulletin A^o. 66, University of Illinois, November, 1901. 



FUNCTIONAL VARIATION 



79 



Rose commenced April 13 and Nora, May 22, 1899, and both 
were milked for a full twelve months. Both were in good health, 
and both continued in good flow until the last, Rose averaging 
over 18 pounds of milk per day and Nora nearly 14 pounds for 
the last seven days of the test. Each consumed all the feed she 
cared to take, the only restriction being that its composition 
was the same for both. Neither was in any sense beefy, but 
Rose gained 181 pounds and Nora 165 pounds from August i 
to April I, showing that they were evidently working at or near 
their limit of milk production. The grain fed was corn meal 
and oil meal, and the roughage consisted of clover hay, rape, 
green corn, and corn silage, always in combination with one or 
more of the following, — gluten meal, wheat bran, and ground 
oats. They were never on pasture during the experiment, and, 
as has been stated, the feed was identical in quality for both. 

Rose consumed slightly the heavier ration and yielded decid- 
edly the larger product both in milk and fat. The following 
table exhibits the total feed consumed and the product yielded 
for the entire period of twelve months : ^ 

Comparative Milk Production on Basis of Food Consumed 



Cow 


Feed ' 


Milk 


Fat 


Butter ' 


Rose 

Nora 


6477.92 
6189.06 


11,329.00 

7,759.00 


564.82 
298.64 


658.95 
348.41 


Difference .... 
Per cent .... 


288.86 
4.67 


3,570.00 
46.01 


266.18 
89.13 


310-54 
89.13 



Cast in verbal form this means that Rose was able to produce 
47 per cent more milk and 89 per cent more butter than Nora, 
with the consumption of but 4.67 per cent more feed. Reduc- 
ing both to the same basis of food consumed, it appears that 
with a given amount of feed fo7- every WO pounds of milk giveti 
by Nora, Rose gave IJQ.§ founds ; a7id for every 100 pounds of 

1 Feed in pounds of digestible nutrients. Butter reckoned at 16.66 per cent 
water, adding one sixth to the butter fat. Per cent of difference calculated on 
Nora as a base. 



8o VARIATION 

butter fat {or butter) produced by Nora, Rose produced iSo.y 
pounds. For purposes of milk production, therefore, feed was 
worth 39.5 per cent more when fed to Rose than when fed to 
Nora, and for butter production it was worth 80 per cent more. 
This, then, is the true measure of the functional difference 
between these two cows, and it is good and sufficient ground 
on which to base breeding operations. Further, it is to be noted 
that this is not the difference between .a good cow and a poor 
one but between two good cows; for Nora produced 348.4 pounds 
of butter, which, as Professor Fraser remarks, is nearly three 
times the average yield (130 pounds) of cows in the United 
States, and almost one half more than the average yield (250 
pounds) of what are considered profitable cows in Illinois. 

It may be added at this writing (1906) that Rose, though used 
in many experiments and exhibited at various state fairs and 
at the St. Louis Exposition, is still living, hale and hearty at 
sixteen years of age, and is still an economical producer of milk. 
She has an average yearly record of J84 pounds of butter fat 
for ten years, ^ and though she has been in many tests since the 
one just reported she has never been beaten but once. That 
was in the following case, which bears further on the present 
point. Three cows were in this test with Rose, — Tina Clay's 
Queen, known to be a poor cow, and two natives, known as 
No. I and No. 3, supposed to be two of the four best cows bought 
for experimental purposes out of a herd of one hundred. Reduced 
to the same feed basis, and taking the yield of Queen as 100, 
that of No. 3 would be represented by 121, of Rose by 304, and 
of No. I by 312. This is a rate of more than three to one against 
the poor cow, or over tzuo and one-Jialf to one betiveen good coivs 
on tJie same feed basis. 

This difference in the efficiency of individual cows is depend- 
ent not so much upon daily differences as upon the ability for 
long-time performance. Some cows will give a heavy yield for 
three or four months, and go dry in six or seven months ; others 
will give a profitable yield almost continuously. Both extremes 
are deceptive. The herdsman will almost certainly overrate the 

1 Since the above was written Rose has completed a twelve-year record of 7258 
pounds of milk and 360 pounds of butter fat as an average. 



FUNCTIONAL VARIATION 8l 

former and underrate the latter, so prone are we to remember 
striking and maximum data. 

These are not isolated and peculiar cases. Professor Fraser 
of the University of Illinois tested 554 cows in 36 commercial 
dairy herds of the state for a full period of twelve months each. 
He found that the best 25 per cent of the whole number tested 
were able to produce an average of 301 pounds of butter fat per 
year, while the 25 per cent of lowest efficiency were able to pro- 
duce an average of but 133.5 pounds, — a range of consid- 
erably more than two to one. The practical significance of this 
difference is pointed out by Professor Fraser as follows : If it 
costs thirty dollars a year to feed the poorer cows and thirty- 
eight dollars a year to feed the better ones, then at present prices 
a herd of twenty-five of the latter will produce as much net profit 
as would a thousand of the former. A little calculation will show 
the immense saving in labor in keeping the smaller herd, and, what 
is equally significant, the relatively smaller investment in animals, 
feed, and barns, and the smaller volume of business generally. 

The faculty of producing a high yield of milk manifestly 
depends not only upon the activity of the mammary glands but 
also upon the capacity of the stomach to handle a large amount 
of feed, and the ability of every organ of the body to discharge 
its normal functions regularly and to endure the wear and tear 
of sustained exertion under heavy pressure. This particular 
function of milk production is, therefore, a kind of resultant or 
algebraic sum of many body functions, and we should not expect 
to find its maximum except rarely and in few individuals. A 
simpler function practically independent of others would there- 
fore be unhampered by their weaknesses, and it would reach its 
maximum in a higher proportion of individuals. 

Variation in meat production. That the same principle is 
operative in meat production is abundantly shown by experi- 
ments. Steers were fed separately from calfhood to full maturity 
at the Michigan Experiment Station. ^ The experiment was com- 
menced as a breed test by Professor Samuel Johnson, and com- 
pleted by the writer as a test of individual differences in ability 
to put on gain in proportion to feed consumed. 

^ Bulldtiii A'o. 6g, Agricultural E.xperiment Station, Michigan. 



VARIATION 
Gain in Proportion to Feed Consumed 



Steer 


Weight at Beginning 


Pounds of Gkain to 
One of Gain 


Jumbo 

Colby 

Walton 

Nick 

Milton 

Boy 

Barrington 

Disco 


650 
840 

S70 
740 
920 
485 
605 
440 


6.16 
6.08 
7.00 
6.30 
6.48 
4.56 

4-93 
4.78 



Differences of this character are further shown by Professor 
Mumford's experiments with the various market grades of steers.^ 
Feeding cattle are divided in the markets into six grades, from 
fancy selected down to inferior. A car load (sixteen) of each of 
these six grades (ninety-six animals in all) were fed on the same 
ration for a period of 179 days. The animals were all natives, 
though the better grades showed a much higher percentage of 
good blood than did the lower. The following table shows the 
relative ability of these six grades of steers to handle feed and 
convert it into gain : 

Rel.ative Efficiency of Different Grades of Steers 



Grades 


Gain per 
Steer 


Total Gain 

16 Steers 


Total Dry Mat- 
ter Consumed 


Dry Matter per 
Pound of Gain 


Fancy 

Choice 

Good 

Medium .... 
Common .... 
Inferior .... 


460 

455 
419 

381 
395 
350 


7362 
7284 
6705 

6095 
6322 
5607 


73.267 
88,093 
81,017 
79.535 
75.S75 
72,494 


9-95 
12.09 
12.08 

13-05 
12.00 
12.93 



Here is a variation of over 31 per cent (460-350) in the total 
gain of sixteen steers under equal opportunities, and, what is 



1 Bulletin xVo. go. Agricultural Experiment Station, University of Illinois. 



FUNCTIONAL VARIATION 



83 



more significant, a difference of over 30 per cent in the feed 
required for a pound of gain. This shows the inferior feeding 
quahty of the lower grades, due partly to age and partly to lack 
of breeding. 

Composition of corn as influenced by functional deviation. One 
hundred and sixty-three good seed ears were selected from a 
strain of corn known as Burr's White. ^ They presented to the 
eye no more differences than are usual with seed corn. Three 
rows of kernels from each were analyzed for protein and also 
for fat. As a result the protein in the various ears was found 
to range from 8.25 per cent to 13.87 per cent and the fat from 
3.84 per cent to 6.02 per cent. 

Composition of Corn from 163 Different Ears 



Corn 








Carbo- 


Corn 








Carbo- 




Ash 


Protein 


Fat 




A 


SH 


Protein 


Fat 




No. 








hydrates 


No. 








hydrates 


76 


1.70 


10.05 


4-77 


83.48 


104 I 


54 


11.82 


4-43 


82.21 


77 


1-45 


10.42 


5.24 


82.89 


105 I 


2,7 


12.36 


4.84 


81.43 


78 


1-55 


11.00 


4.90 


82.55 


106 I 


33 


II. 15 


5.21 


82.31 


79 


1.62 


10.89 


4.88 


82.61 


107 I 


33 


9-47 


4.97 


84.23 


80 


1.63 


I 1.50 


4-58 


82.29 


108 I 


30 


11.04 


4.67 


82.99 


81 


1.47 


11.49 


4.26 


82.78 


109 I 


45 


10.82 


5.65 


S2.08 


82 


1-39 


I 1. 78 


4-83 


82.00 


IIO I 


60 


12.81 


5.21 


80.38 


83 


1. 17 


9.08 


4.05 


85.70 


III I 


31 


10.76 


4.13 


83.80 


84 


1-51 


12.79 


4.25 


81.45 


112 I 


26 


10.48 


4.54 


83.72 


85 


1.46 


11.76 


4.94 


81.84 


113 I 


10 


9.30 


4-38 


85.22 


86 


1.50 


12.07 


4.61 


81.82 


114 I 


32, 


9.12 


4.10 


85-45 


87 


1-59 


12.40 


4-74 


81.27 


"5 I 


29 


10.41 


4.17 


84.13 


88 


1-35 


9-34 


4.84 


84-47 


116 I 


10 


8.38 


4-88 


85.64 


89 


1.61 


10.71 


4.70 


82.98 


117 I 


42 


9-95 


4-23 


84.40 


90 


1-55 


9.90 


4-97 


83-58 


118 I 


44 


11.40 


5.02 


82.14 


91 


1.56 


10.68 


4.91 


82.85 


119 I 


55 


12.38 


4.62 


81.45 


92 


1.46 


12.96 


3-97 


81.61 


120 I 


39 


9-97 


4.42 


84.22 


93 


1.48 


11.80 


4.80 


81.92 


121 I 


36 


10.09 


4.82 


83-73 


94 


1.74 


11.89 


4-55 


81.82 


122 I 


36 


10.31 


5.25 


83.08 


95 


1-55 


10.49 


5-51 


82.45 


123 I 


34 


9.68 


4.01 


84.97 


96 


1.60 


II. 10 


4.38 


82.92 


124 I 


44 


11.87 


4.61 


82.08 


97 


1-59 


11.84 


4.96 


81.61 


125 I 


34 


10.73 


4-53 


83.40 


98 


1-39 


10.23 


5-51 


82.87 


126 I 


49 


13.87 


5-72 


78.92 


99 


1.42 


8.40 


4.91 


85.27 


127 I 


43 


"•53 


4.31 


82.73 


100 


1.65 


12.28 


4.76 


81.31 


128 I 


33 


11.64 


4.57 


82.46 


lOI 


1.30 


10.08 


4.86 


83.76 


129 I 


36 


11.25 


4.16 


83.23 


102 


1.49 


11.83 


4.51 


82.17 


130 I 


35 


11.86 


5.01 


81.78 


103 


1.44 


11.25 


4.78 


82.53 


131 I 


47 


10.49 


4.86 


83.18 



1 This was the foundation of Dr. Hopkins' work in corn breeding at the Uni- 
versity of Illinois, as reported in Bulletin Xo. 55 and Bitlletin Xo. 100. It will be 
further discussed later on. 



84 



VARIATION 



CoMPOsn 


ION OF 


Corn 


FROM 163 DH'FERENT EaRS - 


— Continued 


Corn 


Ash 


Protein 


Fat 


Carbo- 


Corn 


Ash 


Protein 


Fat 


Carbo- 


No. 








hydrates 


No. 








hydrates 


132 


1-55 


II. 13 


4-55 


82.77 


186 


1.48 


10.78 


4-74 


83.00 


^33 


1-39 


II. 13 


4.10 


83-38 


187 


1.28 


10.49 ■ 


4-44 


83-79 


134 


1.30 


10.85 


4-45 


83.40 


188 


'•53 


13.10 


5-51 


79-86 


135 


1-37 


11.29 


4-53 


82.S1 


189 


1.32 


9-58 


5-63 


83-47 


136 


1.59 


"•43 


5.10 


8 1. 88 


190 


1-25 


11.50 


4-95 


82.30 


'^l 


1.47 


II. 61 


4.41 


82.51 


191 


1.29 


II. 19 


4-31 


83.21 


138 


,.36 


1 1.36 


4-53 


82.75 


192 


1-51 


11.49 


4.07 


82.93 


139 


1-57 


9.81 


5-23 


83-39 


193 


1.36 


9-47 


4.51 


84.66 


140 


1-34 


IO-53 


4.18 


83-95 


194 


1.50 


11.47 


4.65 


82.38 


141 


1-45 


12.42 


4.51 


81.62 


195 


1.54 


11.09 


4-37 


83.00 


142 


1-37 


931 


4.82 


84-50 


196 


1.30 


9-44 


3-95 


85-31 


143 


1.29 


11-33 


4-49 


82.89 


197 


1.26 


11.20 


4.46 


83.08 


144 


1.42 


11-39 


4.99 


82.20 


198 


1.44 


10.23 


4-53 


83.80 


145 


1-45 


8.25 


4.81 


85.49 


199 


1.29 


10.64 


4.67 


83.40 


146 


1.47 


11.29 


4-83 


82.41 


200 


1-39 


10.13 


4-84 


83.64 


147 


1.26 


12.21 


4-49 


82.04 


201 


1.38 


9.64 


5.22 


83.76 


148 


1-54 


11.94 


4-74 


81.78 


202 


1-39 


11.26 


4.96 


82.39 


149 


1.36 


11.29 


4.08 


83.27 


203 


1.26 


10.48 


4-59 


83.67 


150 


1.44 


11.71 


4-03 


82.82 


204 


1.66 


12.57 


4.82 


80.95 


151 


1.40 


9-31 


496 


84-33 


205 


1.46 


10.71 


5-36 


82.47 


152 


1.41 


11.90 


4.09 


82.60 


206 


1-34 


10.27 


4-65 


83.74 


153 


1-35 


12.51 


5-I9 


80.95 


207 


1-25 


11.09 


4.27 


83-39 


154 


1.42 


II. 13 


5.02 


82.43 


208 


1. 48 


12.05 


4.78 


81.69 


155 


1.44 


1 1.05 


4-53 


82.98 


209 


1. 48 


10.22 


4-30 


84.00 


156 


1-39 


11.74 


4.14 


82.73 


210 


1-45 


II. 16 


4-75 


82.64 


157 


1.46 


10.02 


4.88 


83.64 


211 


1.48 


10.44 


4.21 


83.87 


158 


1.45 


10.66 


4-51 


83-38 


212 


1.27 


9-75 


4.12 


84.86 


159 


1.48 


11-53 


465 


82.34 


213 


1-53 


12.40 


4-75 


81.32 


160 


1-43 


11.50 


4-83 


82.24 


214 


1.58 


10.22 


4-43 


83-77 


161 


1.47 


II. II 


4-93 


82.49 


215 


1-45 


9.22 


4.60 


84-73 


162 


1.48 


12.09 


5-6i 


80.82 


216 


1.42 


10.27 


4-35 


83.96 


163 


1.29 


10.78 


5.09 


82.84 


217 


1.32 


9-39 


4-83 


84.46 


164 


1.30 


9-36 


4-34 


85.00 


218 


1.40 


9-74 


4.71 


84.15 


165 


1.47 


10.50 


4-75 


83.28 


219 


1-37 


9-92 


4-32 


84-39 


166 


1.65 


11.29 


3-84 


83.22 


220 


1-43 


9-63 


5-23 


83-71 


167 


1-37 


9-58 


4.72 


84-33 


221 


1.32 


10-33 


5.01 


83-34 


168 


1.49 


10.94 


4-34 


83-23 


222 


1.41 


12.34 


4-57 


81.68 


169 


1.60 


11.79 


4.22 


82.39 


223 


1-49 


10.58 


4.64 


83.29 


170 


1.36 


11.06 


4-39 


83.19 


224 


1-52 


11.36 


4-63 


82.49 


171 


1.44 


II. 18 


5-75 


81.63 


225 


^■33 


9-15 


4-55 


84.97 


172 


1-45 


12.28 


3-99 


82.28 


226 


1.36 


10.31 


5.08 


83-25 


173 


1-39 


10.14 


4-35 


84.12 


227 


1.46 


12.63 


5-15 


80.76 


174 


1.30 


10.19 


5.22 


83-29 


228 


1.41 


12.16 


4.12 


82.31 


175 


1.40 


12.68 


5-29 


80.63 


229 


1.36 


11.04 


4-52 


83.08 


176 


1-37 


9.86 


4-73 


84.04 


230 


1-43 


12.10 


4.29 


82.18 


177 


1.48 


13.06 


4-93 


80.53 


231 


^•33 


10.95 


4.60 


83.12 


178 


1-37 


10.93 


4.76 


82.94 


232 


1.52 


12.76 


4.10 


81.62 


179 


132 


11.87 


5-03 


81.78 


233 


1.40 


9-75 


4.14 


84.71 


180 


1-39 


11.27 


4-55 


82.79 


234 


1-39 


10.78 


4.76 


83.07 


181 


1.47 


9.66 


4.21 


S4.66 


235 


1.58 


9-97 


5.27 


83.18 


182 


1-37 


10.97 


3-94 


83.72 


236 


1.40 


10.18 


6.02 


82.40 


183 


1-54 


10.32 


5-46 


82.6S 


237 


1.47 


II. 16 


5-13 


82.24 


184 


1.44 


10.68 


4.89 


82.99 


238 


1.60 


11.42 


5.20 


81.78 


185 


1.42 


9-33 


4.49 


84.76 













FUNCTIONAL VARIATION 



85 



The wide variation in all constituents, particularly in protein 
and fat, indicates that profound differences existed in the func- 
tional activities of the plants that produced these ears. In order 
to determine whether these differences are constitutional and 
therefore hereditary, the twenty-four ears highest in protein 
were planted (separately) for the "high protein plot" and the 
twelve lowest for the "low protein plot." In the same way the 
twenty-four highest and the twelve lowest in fat were planted 
for "high fat" and "low fat," respectively. This has been 
continued from its beginning in 1 896-1 897 until the present 
(1907), and is still in progress, the practice being each year to 
plant separately the ears that show the highest and the lowest 
values in respect to these particular constituents. The follow- 
ing table shows the average composition of the seed corn and 
the crop for the first year of the experiment: 

Protein 



Highest protein ear out of 163 analyzed 

Lowest protein ear out of 163 analyzed 

Difference 

Average of 24 high protein ears planted 
Average of 12 lovv' protein ears planted 
Difference 

Average of crop from high protein seed 
Average of crop from low protein seed 
Difference 



13-87 
8.25 
5.62 

12.54 
9-°3 
3-51 

1 1. 10 
IO-55 

•55 



Fat 

Highest fat ear out of 163 analyzed 6.02 

Lowest fat ear out of 163 analyzed 3.84 

Difference 2.18 

Average of 24 high fat ears planted 5.33 

Average of 1 2 low fat ears planted 4.04 

Difference 1.29 

Average of crop from high fat seed 4.73 

Average of crop from low fat seed 4.06 

Difference 67 



86 VARIATION 

It is sufficient for the present purpose to note that there was 
a difference of 5.62 per cent (13.87-8.25) in the protein content 
of the highest and the lowest ears of the 163 analyzed ; of 3.51 
per cent (12.54-9.03) in the seed planted; and of 0.55 per cent 
( 1 1. 18-10.55) in the crop harvested the first year. 

It is not the intent to pursue this subject further at this 
point. It will be fully discussed under heredity and under plant 
breeding, but enough has been quoted to show that these func- 
.tional differences are both distinctive and hereditary, and that in 
it all the ear is the unit to such an extent that it is entirely prac- 
ticable to permanently influence functional differences by selec- 
tion. Indeed this has been done already to such an extent that 
corn has been produced with a higher protein content than wheat. 

Variation in sugar production. Sugars of various kinds are 
produced by many plant and animal activities. Certain plants 
excel in this particular function, and among these wide differ- 
ences have been found, leading to marked and permanent in- 
crease in the amount of sugar produced. The beet, for example, 
though originally producing but from 4 to 6 per cent of sugar, 
has been so improved and its sugar-producing activities have 
been so increased as to yield specimens containing as high as 
25 per cent of sugar and whole crops averaging 14 per cent. 

Cane is also variable, and every one familiar with the maple 
knows that certain trees will yield a large amount of exceed- 
ingly sweet sap, while others yield but little, which little may 
be either sweet or tasteless, — indeed, even bitter. 

Variation in speed, scent, and organic activities generally. 
One horse is faster or more enduring than another, not so 
much from conformation as from inherent activity and power 
of endurance. Some dogs are especially keen in scent, others 
are defective, and the hearing instinct is much better developed 
in some individuals (dogs, cats, horses, cattle, birds, etc.) than 
in others.^ 

Mental qualities, personal tastes, and intellectual ability in 
general are conditioned not upon conformation but upon the 

1 It is more than likely that some of these differences are connected with the 
degree of development of certain portions of the nervous system. They are 
none the less functional, however. 



FUNCTIONAL VARIATION 87 

peculiar action of certain parts possessed by the race in com- 
mon, but whose special functioning in each particular case 
determines the place of the individual in the scale of life. 

Variation in vital functions. For present purposes the animal 
body may be regarded as a colony of organs, each endowed 
with its own peculiar function, the life of the whole and of 
every member being dependent upon the degree of success 
with which each portion does its work. The whole is, therefore, 
as strong as its weakest member, and when the whole is put to 
work in service for man, that service will depend not only upon 
the functional activity of the special organ involved, as the 
udder or the muscular system, but also upon the successful 
discharge of all vital functions when subjected to the unnatural 
strain involved in working under pressure. The point at which 
the machine will break down or fail to do successful work is, 
therefore, a matter of relative strength of parts, and in the last 
analysis the limiting element in performance is not infrequently 
one or more vital functions, which experience shows are as 
variable as are other and, from the biological standpoint, less 
important characters. 

The beat of the heart, in man for example, though steadily 
decreasing in rapidity from infancy to old age, yet varies be- 
tween different individuals at maturity all the way from less 
than fifty to more than eighty beats per minute. Athletes tell 
us that the slow beat is characteristic of long-distance running 
and sustained effort generally, but that individuals of this order 
are ill adapted to short-distance running or other work requiring 
quick response to stimulus. 

There is a marked difference in the digestive powers of 
different animals, and some individuals starve because the 
stomach and intestines are unable to dissolve sufficient food to 
meet the demands of the body, — and there are all degrees of 
starvation.^ Others with excellent digestion but with limited 
powers of assimilation fail to make use of the full supply that 

^ Wide study of men, animals, and plants will reveal many cases in which the 
individual has accustomed itself to an abnormally small food supply. The effect 
is not necessarily fatal, but it is shown in reduced output either of labor, body 
product, or other form of organic activity. 



88 VARIATION 

is put into the circulation. In the- case of Rose and Nora, pre- 
viously cited, what did Nora do with the excess of food con- 
sumed ? Digestion experiments with individuals indicate no such 
differences in digestion among healthy animals as the differences 
in milk yield that are known to exist between cows. The only 
conclusion is that in a case like this the surplus food passed on 
out of the body, laying excessive labor upon the excreting organs 
as well as incurring loss upon the one who provided the feed.^ 

From this it will be seen that the excreting organs them- 
selves act as a kind of safety valve, and that much depends 
upon their relative ability to discharge their functions well. 
This they are better adapted to do in some individuals than in 
others, but that every effort is made to keep up with demands 
is evidenced by the fact that if one kidney is lost the other 
acts for both, usually increasing in size. Speaking generally, a 
cow will give as much milk from three teats as from four. 
Whether this is from compensation, as with the lost kidney, or 
whether it is true only because cows are seldom worked up to 
their limits, the data at hand do not determine. 

The tremendous increase in the activity of the salivary glands 
on the part of tobacco chewers, the increase in size of muscles 
through use, and the marvelous development of skill in eye and 
hand by long-continued practice, as in the playing of musical 
instruments, reading on the part of the blind, etc., — these are 
all familiar examples of functional development through prac- 
tice. That this development is or may be greater in some indi- 
viduals than in others is too well known to need more than 
passing mention in this connection. 

Resistance to disease and invasions of the animal economy 
generally differ greatly in different individuals. Some are abso- 
lutely immune to certain diseases, others peculiarly susceptible. 

It is a matter of common observation that in fields of corn 
killed by frost an occasional stalk remains green and unaffected, 
showing unusual powers of resistance, due to some constitu- 
tional difference. Without a doubt these are the differences 

1 This is conclusive proof of the fact that appetite is not a safe guide to the 
amount of food that can be profitably consumed. The most that can be said is 
that it is a good indication of body use among animals whose efficiency is known. 



FUNCTIONAL VARIATION 89 

that go far toward constituting the essential distinction between 
annuals and biennials in temperate regions. 

And so it is that the value of an animal or a plant depends 
not only upon what it can do but also upon its powers to endure 
sustained exertion ; and this is indirectly dependent upon the 
vital functions, which are therefore of prime consequence to the 
farmer. The horse that died in a Michigan coal mine at fifty- 
four years of age after having worn out more than five genera- 
tions of harness mates ; Old Granny, the Galloway cow that 
died at nearly thirty-six years of age, having raised no fewer 
than twenty-five calves ; men who live to be a hundred or 
thereabouts, — these are examples not of individuals that have 
been shielded from hardships, but rather of those splendid 
pieces of animal machinery whose every part easily performs its 
proper function to any limit laid upon it by the exigencies of 
life.^ That these functional differences exist and that they are 
in a measure hereditary are facts that challenge the most careful 
attention of the thoughtful breeder. 

1 Benjamin Franklin Harris died of pneumonia in Champaign, Illinois, May 7, 
1905, at the age of ninety-three years, four months, twenty-two days. He was 
personally known to the writer as remarkable not so much for his advanced age 
as for the fact that he was in full possession of all his powers, and actively 
engaged in business until within a week of his death. He organized the First 
National Bank, which at his death was operated by three generations of the 
Harris family ; but he was president to the last in fact as well as in name, and 
the management deferred to his judgment even in matters of detail. 

He was the owner and operator of over five hundred acres of prairie land, and 
was one of the earliest and largest cattle men in the Middle West. He was a 
noted feeder before a market was established in Chicago, and was both a buyer 
and a seller on that market every year of his life afterward. He was always a 
believer in heavy cattle, and he finished and sold the one hundred heaviest cattle 
ever marketed in this country and, so far as is known, in the world, — an achieve- 
ment of which he was always especially proud. 

This instance of longevity is given not as an extreme in respect to years but 
in respect to retention for so long a time of all the powers of body and mind. 
Mr. Harris never had a second childhood, and was a good example of what 
a splendid machine is the human organism, which ordinarily breaks at the 
•weakest point but does not wear out. How full of weak points animal organ- 
isms really are and how weak these points must be are considerations forced upon 
the mind by the fact that Mr. Harris' span of life was more than three times that 
of the average man. These three instances of extreme longevity in animals and 
man, showing what is possible in animal life, afford to the breeder ample food for 
reflection. 



90 VARIATION 

Variation in fertility. Certain birds regularly produce two 
eggs, others three, and still others four, before incubation. The 
average hen, following her natural habit, lays a "setting" 
(ten to fourteen) and then suspends for incubation. The " crop " 
of ova has been laid, and time is required for another to come 
forward. The Maine station, however, has succeeded in greatly 
increasing the production of eggs, and has produced one hen that 
has laid two hundred and fifty-one eggs during a single year. 

Most cows produce only five or six calves, many only one or 
two, and some not any, yet Old Granny (No. i in the Galloway 
Herd Book) produced twenty-five, the last one in her twenty- 
ninth year. The difference between regular and shy breeders 
is the difference in the functional activity of the reproductive 
organs, and next to performance ability it is the most impor- 
tant character in the eyes of the breeder. Even longevity itself 
is not its equal from the standpoint of the improver, because 
quality cannot be said to exist in the race unless the individuals 
that possess it are sufficiently fertile to insure its easy and 
certain perpetuation. 

Accumulation of functional variations. Having shown the 
marvelous differences in functional activity between different in- 
dividuals, and having shown that these differences are hereditary, 
as in corn, it follows necessarily that functional variations may be 
accumulated into true breed distinctions, and that strains of 
animals and plants may be permanently established with exceed- 
ingly high efficiency in desired lines ; indeed, this has been already 
accomplished, though we are still far short of what is possible. 

For example, the beef breeds are more economical producers 
of meat than are the dairy breeds, and the converse is true as 
to milk production. These two functions have, therefore, been 
largely separated along breed lines. But it cannot be said that 
one beef breed is more efficient than another in meat produc- 
tion, or that any one dairy breed stands out preeminently as 
the most economical producer of milk. This is partly because 
breed differences have been largely built up along lines other 
than those of efficiency, and partly because all breeds contain 
many individuals of low efficiency in their own breed characters 
and high efficiency in those of other breeds. Some Jerseys, 



FUNCTIONAL VARIATION 9 1 

therefore, are better feeders than certain shorthorns, and there 
are to be found among the latter breed individuals that are 
more economical producers of milk than are many of the Jer- 
sey breed. 

It has been said that no race was ever taken by a part-bred 
horse over one that was racing bred. Whether literally true or 
not, it is substantially correct, so intensely have the racing 
ability and instinct been developed in certain breeds. 

These facts, together with what is known as to corn and beets, 
show clearly that much yet remains to be done in the way of 
developing functional activity, thereby increasing efficiency. 

SECTION II — VARIATION IN THE DEGREE OF ACTIVITY 
OF NORMAL FUNCTIONS WITHIN THE SAME INDIVIDUAL 

Of no less scientific or economic interest than the data given 
in the last section is the fact that functional variation is by no 
means confined to differences between individuals. The prin- 
ciple applies, though to a less extent, to the individual itself, 
whose activities are not constant but variable from day to day 
and throughout its life. 

Daily fluctuation in normal functions. It will be found upon 
investigation that the ordinary functions of the body are unex- 
pectedly irregular. Even the heart action is not absolutely 
constant ; it is slower when the body is at rest than when it is 
in action and is subject to great acceleration in certain diseases. 

All organs of the body work better some days than others ; 
indeed, there is a distinct periodicity with each, — a period of 
increase, followed by one of maximum activity, and that again by 
one of subsidence. This is the way organs rest. These periods 
are evidently of different lengths, and it is therefore only occa- 
sionally that the body as a ivJiolc is at its maxiimini. A good 
example of this periodicity with functional deviation from day to 
day is, again, that of milk secretion, which, as has been remarked, 
is a kind of resultant of all the activities of the body. The fol- 
lowing table gives the variations in the quantity and character 
of milk from a single cow for a period of one month. ^ 

1 Bulletin No. ^i^ Agricultural E.xperiment Station, University of Illinois. 



92 



VARIATION 




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FUNCTIONAL VARIATION 93 



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94 VARIATION 

Comment is hardly necessary to show the irregular working 
of the animal machine, which in this case was a mature, strong, 
and healthy cow. The per cent of fat varied all the way from 
2.7 to 4.2 within the space of twenty-four hours. 

Influence of age upon functional activity. At birth the 
vital functions and those of growth are at their maximum. At 
this time growth seems to be proceeding with the " energy 
of embryonic development." It continues at a maximum for a 
time,^ gradually declining in rate until maturity, when growth 
of the general body ceases, although for certain parts (hair, 
teeth, horn, hoof, reproductive cells, etc.) it continues nearly or 
quite through life. In case of accident many parts not com- 
monly indulging in growth after maturity are able to regenerate 
with more or less success (bone, skin, blood vessels, nerves), 
but among the higher organisms generally growth practically 
ceases at maturity.^ It is for this reason that feeding enterprises 
are most profitable with young animals that are still growing. 
At this age functional activity is greater and general bodily 
efficiency higher. 

One reason why the lower grades of feeders are less econom- 
ical producers than the better grades is that the animals are 
older, the difference in age between fancy selected and inferior 
steers being one to two years. 

Strength and endurance are evidently at their maximum 
somewhat after maturity, although with the passing of that 
age is also lost something of the power of rapid recuperation 
and repair. 

The reproductive functions, undeveloped until a considerable 
period after birth, attain a high degree of energy, if not their 
maximum, somewhat before full maturity is reached. They then 
decline, and fail entirely in old age. Their duration is therefore 
considerably less than the life of the individual, often dropping 
below 50 per cent of the full life period. 

1 The curve showing rate of growth at different ages has not been sufficiently 
worked out, but enough has been done to indicate that the maximum rate of 
growth is attained a few days after birth and that this maximum is never again 
reached. 

- Trees continue to increase in size, to some extent at least, during life, illustrat- 
ing a marked difference between the higher plants and animals. 



FUNCTIONAL VARIATION 95 

At what period the reproductive functions are most success- 
ful in producing young of a high order of excellence, whether in 
youth, middle age, or old age, is not determined, though it is a 
point on which light is badly needed. It is certain that the 
practice of using young and immature sires is almost universal, 
especially among cattle. That there is danger in continued 
reproduction from immature animals, even though they are sex- 
ually vigorous, there is grave reason to fear, and yet, in general, 
reproduction antedates maturity. 

The duration of profitable service depends, of course, upon 
the nature of the function involved. The life service of a racing 
horse is manifestly less than that of a work horse, and the life of 
a meat animal is less than that of one kept for milk. 

Influence of exercise: use and disuse. The beneficial effect of 
use in developing and perfecting the functions of the body has 
been recognized from the most ancient times. Athletes train 
for this purpose. Musicians practice for many hours every day ; 
indeed their chief labors arise from the need of constant and 
severe exercise of the musical faculties in order to achieve any 
considerable degree of perfection and to hold it after it has 
been acquired. 

Horses designed for racing are worked almost from the first 
in order to make the most of any natural ability to trot or run. 
Cows are believed to be more efficient producers of milk if they 
begin at two years of age and are kept, so to speak, in constant 
practice, and barrenness is believed to be less likely if heifers 
are bred early than if left to attain maturity without produc- 
ing young. 

Darwin discovered that the wing bones of wild ducks as com- 
pared with their leg bones were relatively heavier than those of 
tame ducks, corresponding to their respective habits of life. 
The arm of the blacksmith and the wing of the ostrich ; the 
remarkable leg of the kangaroo and the remains of that of the 
whale ; the brain power of the busy man and that of the slug- 
gard, — these and scores of examples that might be cited show 
not only that exercise develops, quickens, and perfects the body 
functions, but they show, too, that their very retention or loss 
depends in the long run upon their constant and rational use. 



96 VARIATION 

Blind people acquire a quickened and an educated sense of 
hearing and a touch that amounts almost to a separate sense. 
In the same way the developing of the bodily functions and 
activities generally depends upon judicious use (exercise) ; and 
the skill of the trainer and the results he is able to achieve 
depend not only upon his knowledge of methods that will most 
certainly insure the exercise of the desired parts but also upon 
his judgment as to how severe and protracted that exercise 
should be in order to secure the maximum effects of use and 
not incur the destructive consequences of overuse. This is as 
true in the feeding yard as upon the race track, and applies as 
well to the raising of good and profitable feeders as to the devel- 
oping of racing horses, the education of drivers and saddlers, the 
training of hunting dogs, the " trying out " of homing pigeons, 
or the teaching of canaries to sing by never allowing the young 
birds to hear a false note. 

Influence of feed upon functional activity. The relation of 
the amount of feed to its economical consumption is a subject 
needing careful investigation. Enough is known to warrant the 
assertion that animals can and do learn to take amounts far 
larger than can be really used. When a steer consumes over 
a bushel of corn a day he has simply formed the eating habit 
as the result of a morbid appetite, nor is this appetite an indi- 
cation of body needs or a guaranty of its powers to economically 
convert the feed into meat, milk, or labor. 

It is significant that steers very gradually brought into full 
feed will never take these enormous amounts. Professor H. W. 
Mumford of the University of Illinois finds that under such cir- 
cumstances twenty pounds of grain per day is all the animal 
will take. 

Consumption of extreme amounts is, therefore, evidence only 
of the quantities of feed the digestive tract can carry and dis- 
charge without calamity, of its power to secrete gastric and 
other digestive juices, and of the ability of the excreting organs 
to eliminate unused and unusable surplus from the body 

In the case of Rose and Nora the latter consumed the same 
feed as the former but returned but little more than half as 
much. She was undoubtedly, from the standpoint of economy, 



FUNCTIONAL VARIATION 97 

overfed, but whether the same individual would make cheaper 
returns on less feed is not so well known as it should be. In 
the mechanical world the highest return of energy per unit of 
consumption is realized when the machine is working full but 
somewhat below its maximum capacity. Doubtless the same 
principle holds with living machines, but on this point we are 
sadly in need of accurate information. 

On one point we are certain. The animal (or the plant) is able 
to adjust itself to a wide range of food supply, providing the 
change be gradually made. Not only individuals but whole fam- 
ilies for generations live in a condition of semi-starvation, often 
quite ignorant of their real condition, if indeed they are not so 
indifferent as to prefer to continue in the old way rather than to 
disturb their tranquillity by increased exertion. Such a state 
may easily become chronic in man or animal, but it is unprofit- 
able because all other functions are suspended or reduced to a 
minimum in order that the vital functions may be discharged at 
all and the animal not die outright. There is no nicer problem 
for the stockman and the feeder than this : How much shall I 
put into this animal machine in order to realize the highest net 
efficiency, after first providing for those activities which are 
necessary to the life of the machine, — the vital functions ? 

Influence of hard conditions. Under hard conditions the func- 
tions of life may be disturbed but not destroyed. Under these 
conditions valuable activities are carried forward upon a reduced 
scale, and they often give rise to losses that are no less serious 
because invisible. The most common example of this is in the 
case of ill-fed or much-abused animals and of badly nourished 
crops or trees : some milk is secreted, but it is insufficient and 
its quality is poor ; the plant is weak, with little resisting power 
against insects or disease, and with little ability to mature its 
crop ; the apples are there, but they suffer for the means of 
development. 

Every one who has had experience with unthrifty animals or 
plants knows how difficult and how slow is the process of resto- 
ration of normal activity after it has once been seriously checked 
by neglect or disease. This is because the condition readily 
becomes constitutional, tending to continue through life. 



98 VARIATION 

SECTION III — MODIFICATION OF NORMAL FUNCTIONS 
BY EXTERNAL OR OTHER INFLUENCES 

To what extent are normal functions dependent upon favorable 
environment and how do they respond to changed conditions ? 
A few notable facts will throw some light upon this all-important 
cjuestion. 

Galls. An insect stings a plant. Under the influence of the 
poison a gall is formed. If this gall be shown to a biologist he 
will at once state with certainty the plant which produced the 
gall and the insect that made the injury, so definite in form and 
appearance is the resulting growth and so distinct is it from 
any normal growth of the uninjured plant. 

In other words, specialized plant tissues subjected to a certain 
injury produce a new kind of growth almost as specific as when 
operating under the laws of heredity. Here the functional activi- 
ties of the plant at tJie affected point \\?mq been not dcstroyedXiwX. 
permanently altered m such a manner as to give rise to new struc- 
tures of definite form and often with specific chemical properties, 
as in the case of nutgalls ^ containing 30 to 80 per cent of tannin. 
In cases of this kind a new function has been developed suddenly 
out of old materials, and it at once gives rise to new and distinct 
products, both substantive and morphological. 

Abnormal overgrowth of disordered animal tissues. We have 
just noted that vegetable tissues subjected to specific injuries 
often suffer such a derangement of their functions as to cause 
the production of an abnormal but characteristic overgrowth of 
the injured part. Quite similar is the result of the invasion 
of the animal economy by specific germs from without, as in 
the case of Bacillus tuberculosis. Here the growths (tubercles) 
resulting from the apparent attempt to encyst the foreign material 
are sufficiently characteristic to serve as a name for the disease 
(tuberculosis). 

Tumors generally, whether malignant or benign, are perverse 
overgrowths of normal tissues of the body, whose ordinary 

1 All formulas for good black writing ink include gallnuts (or nutgalls) as the 
characteristic ingredient. Those commonly used are produced on the oak by the 
sting of the gallfly i^Cynips galla-tinctoriie). 



FUNCTIONAL VARIATION 99 

functions have been deranged by some cause, external or inter- 
nal, and whose activities have been diverted to the production of 
abnormal but characteristic tissue with " no typical termination 
to its growth." 

Nearly all tissues of the body ^ are subjected to this derange- 
ment of their ordinary functions, resulting in the suspension of 
all activities except that of growth, which proceeds with the 
"energy of embryonic development" and continues indefinitely. 

Though often supplied with special blood vessels and a system 
of nerves, these growths are entirely functionless and therefore 
useless to the body. Being parasitic they are always a drain 
upon its resources, and often from their nature or position they 
constitute a real menace to its existence. 

A tumor represents a bit of differentiated body tissue that 
for some reason or other has abandoned its characteristic func- 
tions, cut loose from all restraints of heredity, set up an inde- 
pendent existence of its own at the expense of the colony of 
which it has been a respectable and dependable member, and 
has now devoted all its resources to growth, which, as has been 
said, proceeds with the energy of embryonic development, result- 
ing in nothing but functionless masses of living matter, strongly 
suggesting a reversion to primitive undifferentiated tissue. 

Under conditions not well understood all sorts of abnormal 
growths may appear. In this way an antenna may appear where 
an eye ought to be,^ or it may end in a foot instead of a feeler.^ 
The writer knew a young lady of culture and of no little natural 
beauty except for the fact that, growing from one cheek, was a 
tuft of coarse black hair three or four inches long. Her normal 
hair was brown and her complexion clear. What functional dis- 
turbance could have given rise to such a growth is as mysterious 
as it was unfortunate. 

Ossification is a natural process, but under the influence of 
excessive strain it may proceed to an abnormal extent, as in 
spavin, where the entire hock joint becomes solid through the 
ossification of the fluid thrown out as the result of injury. 

^ Muscles, fatty tissue, connective tissue, bone, cartilage, nerves, glands, blood 
vessels, the covering of the brain, etc. 

2 Bateson, Materials, etc., p. 151. i ftp p ^ Ibid. pp. 146-147. 



lOO VARIATION 

Derangements of a more fundamental nature often arise dur- 
ing embryonic development, resulting in monsters of all degrees 
of abnormality. Teratology has little interest to the biologist 
generally, because these abnormal caricatures of life constitute 
nothing but sporadic offshoots of the species. Developing 
from defective germs and having no connection with the line of 
descent, they are of little interest to the evolutionist. Their 
interest to the thremmatologist lies in their bearing upon fiDic- 
tional activity and the degree of certainty with zvJiich specialized 
tissues may be depended upon to discharge their hereditary and 
proper functions. ■ 

Variation due to the suppression or failure of the reproductive 
functions. The abdomen of the crab Carcinus ni(S)ias normally 
has seven segments. In the female these are distinct. In the 
male the abdomen is much narrower, and the divisions between 
the third, fourth, and fifth segments are obliterated. Males, 
however, inhabited by the parasite Sacculina do not develop 
sexual characters, and in them the segmentation is complete, as 
in the female.^ 

A young male is castrated. The parts removed are in no 
sense vital, and they seemingly have no connection with other 
organs of the body. All the bodily functions except those of 
reproduction proceed, bnt not as before. In general the develop- 
ment of the shoulders and neck will be arrested, and they will 
remain lighter and finer. The voice, the nervous temperament, 
the disposition, and the general activity of the body are all 
affected. The mane of horses will be thinner, finer, and shorter. 
The hair of face and neck in cattle will be finer and less curly. 
In hogs the tusks and shoulder plates do not develop. The growth 
of the horns is stopped in sheep, but in cattle the only effect is 
to make them slightly longer and a little more slender, ap- 
proaching the female type. The hinder parts of the body as a 
whole develop rather more in castrated than in entire animals, 
and there is a general approach to the form of the female. It 
is noteworthy in this connection that the same general effect 
follows the failure of the sexual powers with advancing age, 
except that the body development has already taken place. 

1 Bateson, Materials, etc., p. 95. 



FUNCTIONAL VARIATION lOi 

Females deprived of their ovaries develop to some extent the 
characters of the male. Spayed heifers are not at all like bulls, 
but they do resemble steers. Unsexing animals seems, therefore, 
to induce a kind of mediocre development, although it gives rise 
to four distinct types instead of two for each species. 

Many females in later life assume certain characters of the 
male. Cows bellow and paw dirt like bulls ; hens grow spurs 
and try to crow ; women sometimes grow a straggling beard and 
acquire a heavy voice. These changes do not by any means 
appear in all cases, but when they do appear they may be regarded 
as symptoms of loss of the sexual function and of cessation of 
breeding powers.^ 

This influence over the functions of the body by organs 
apparently having no connection with the parts affected is akin 
only to that of certain glands like the thyroid, whose function is 
entirely unknown, but in whose absence children grow up defect- 
ive both physically and mentally.^ We are at this point very 
near to the forces that determine the activities of living matter, 
but the mysteries involved are in no sense cleared up ; they 
rather deepen instead as they are studied. It is as if our vision 
were obstructed, not by a curtain that can be drawn aside afford- 
ing a view beyond, but rather by a solid wall fixing the limits not 
only of vision but of progress as well. 

Functional variation due to the modifying influence of the 
conditions of life. The conditions of life are most active in stim- 
ulating or depressing normal activities, but they are not without 
effect upon their character as well. Plants having a fixed abode 
are more dependent upon their environment and therefore less 
resistant than animals, though species living in confined waters 
are little better off than plants in this regard. 



1 Though bearing but indirectly upon the present que.stion, it is worthy of 
remark at this juncture that many individuals of each sex seem to be naturally 
endowed with more than the usual proportion of the characters of the opposite 
sex and to be correspondingly short in those of their own. Thus we have our 
" mannish " women and our " effeminate " men, distinguished not only for their 
tastes and their mental characteristics generally but for their body conformation as 
well. These abnormal unions of male and female traits are often strange mixtures 
indeed, and may well be avoided in the breeding yard. 

2 Loeb, Physiology of the Brain, p. 207. 



I02 VARIATION 

Plants, and animals too for that matter, growing in cold 
climates or under hard conditions suffer profound changes, to 
which they become accustomed (acclimated) and which are ever 
afterward constitutional. We become accustomed to cold or to heat 
and are thereafter less affected by extremes. Recent calorimeter 
tests show that the temperature of the human body is lowest from 
three to five o'clock in the morning and highest from one to three 
in the afternoon, thus following fairly close the minimum and 
maximum of outside temperatures. These conditions continue 
even if the subject works at night and sleeps in the daytime. 

Two conditions tend to produce hard and spiny growth in 
vegetation. These are intense light and extreme dryness. Both 
are found in tropical regions, and when they occur together their 
maximum results follow as to harshness and spines. These condi- 
tions can be verified in the laboratory, showing conclusively 
that the character of growth is, in a measure at least, dependent 
upon surroundings. 

Speaking generally, plant lice reproduce parthenogenetically 
during the growing season of the summer, and during this time 
only wingless females are produced. With the approach of cold 
weather, however, a winged bisexual brood is produced that lives 
over winter. 

These conditions can be produced artificially in the greenhouse 
at any time by lowering the temperature and allowing the plants 
on which the lice feed to dry up. Thus we may say that wings 
and sex may be developed at will by the manipulation of the condi- 
tions of life. 

The so-called conversion of one species into another by influ- 
encing its environment has been largely overstated, and yet the 
facts are that when Schmankewitsch ^ grew Artcmia salina in 
water whose saline content was gradually increased, the caudal 
fins and their bristles " progressively degenerated " until, in many 
cases, these appendages had disappeared, the animal thus assum- 
ing the character of ^. milJiausenii, which normally lives in waters 
of extreme density. These experiments were undertaken because 
he seemed to have observed this transformation taking place 
naturally in a lake crossed by a dam, and which was inhabited 

1 Bateson, Materials, etc., p. 96. 



FUNCTIONAL VARIATION 



103 



by both species, the one above the other. This dam broke, 
mixing the two species, but in three years original conditions 
were practically restored. The experiments were undertaken 
to learn whether real transformation had taken place or whether 
the result had been brought about by selection. 

The experiment seems convincing, and the point is further 
strengthened by the facts that Schmankewitsch restored the 
caudal fins by reducing the solution, and that when the reduction 
was carried below the normal of A. salina, within three genera- 
tions the last segment of the body divided after the fashion of 
A. branchipus, another related species. The facts are the more 
remarkable as A. salina reproduces parthenogenetically, while 
A. branchipus is not known to do so. 

Biologists are extremely careful not to assume the absolute con- 
version of one species into another by any such direct methods 
as have here been noted, the question being, rather, whether they 
are all good species ; but that single characters are profoundly 
influenced by changed conditions, and come to resemble the same 
character in another and related species, is too well established 
to be longer questioned. What light this may finally throw upon 
the origin of species is problematical, but it serves the present 
purpose in showing the power of environment to profoundly 
modify the functional activities of living beings. 

If a cutting of willow, currant, or other suitable growth be 
planted in the earth, roots will start from the part below the 
ground, and leaves and branches from the part above. If, now, 
it be cut off at the surface of the ground and the top portion be 
planted again, it will again take root at the new point of sever- 
ance which had before borne leaves. The process may be con- 
tinued indefinitely, or until the piece is used up, showing that 
roots or leaves may be developed at will at any point along the 
cutting, according as it is placed below or above ground. 

If a cutting be planted, roots will develop only at the lower end. 
If, however, before planting it be cut into two pieces, each will 
develop roots on the part below ground, and in many species this 
will occur even if the pieces be inverted and planted top down.^ 

1 This is most likely to take place in young wood, less likely in old wood. See 
Morgan, Regeneration, pp. 71-91. 



I04 VARIATION 

A maple tree growing in Urbana had forked into two nearly 
equal parts about six feet from the ground. One part was split 
down and torn off in a heavy storm, when it was seen that roots 
had developed in the crotch and were evidently at work upon the 
soil that had blown from the street and the moisture that had 
accumulated from rains. 

The writer was excavating for a basement. A black cherry 
tree stood some ten feet from the line of the wall. In taking: 
this out many of the roots were severed, their cut ends being left 
in the bank of undisturbed earth. In a few days these cut ends 
were clothed with a growth of green leaves. Here was tissue 
that, under normal conditions, functions only as roots, yet upon 
occasion readily gives rise to both leaf and stem. 

All plants and most animals maintain definite relations to light, 
and if free to move, orient ^ themselves with reference to the 
direction of the light rays striking the surface of their bodies. 
A plant bends toward the window because of the contracting 
effect of the light upon the protoplasm of one side of the stem. 
Many larvae are negatively heliotropic ; that is, the lighted side 
of the body is more irritable and they move away from the light, 
coming to rest only in dark places, where they feed and mature. 
Others are positively heliotropic when hungry and negatively 
heliotropic when fed. Such larvae will climb trees and feed upon 
the leaves or buds until filled, when, becoming sensitive to light, 
they descend and hide in the ground, under rubbish, or in any 
other place shielded from the sun. This action has been errone- 
ously attributed to a semi-intelligent instinct. It is nothing but 
functional dependence upon external stimuli. This is not the 
place to pursue the subject in detail, — which will be done when 
discussing "Instinct and Reflex Action," — but it is the place to 
note the wonderful dependence of certain normal functions upon 
external influences. 

An animal is invaded by a foreign germ and suffers from 
disease. It is in most cases ever after immune to that disease. 
What change has been worked in the animal economy ? We 

1 By orientation is meant the direction in which the long a.xis of the body is 
brought to rest with reference to surrounding bodies or influences, such as grav- 
ity or light. 



FUNCTIONAL VARIATION 105 

know that as long as the white corpuscles are able to discharge 
their proper function the resistance is complete. Why do they 
weary of their work, and what condition is left behind which 
assures absolute resistance to future invasions ? 

The phenomenon of acclimatization in general represents a 
condition in which an organism has undergone a permanent 
change in its vital functions, forced upon it by the exigencies 
of life. In the future studies, however, it will be seen that the 
disturbing effect of adverse conditions, if not too severe, may be 
gradually overcome, and the animal or plant resume its functions, 
either modified or unmodified ; and it will be seen further that if 
the changes be gradual, the immunization will extend to a point 
that would have been fatal at the outset. Thus organisms may 
be reared in a gradually intensified poisonous solution, or in a 
liquid whose temperature is slowly raised, and in this way a point 
may be reached many degrees above the power of normal organ- 
isms to withstand. The subject cannot be pursued further in 
this connection, for it is a large one, with many other bearings ; 
but the student should bear it in mind throughout the study. 

Irregular functioning. An interesting phase of irregular func- 
tioning is found in the so-called "instinctive acts," more properly 
reflex actions, which by popular conception are supposed to pro- 
ceed with unerring accuracy. This assumption is natural in view 
of the complex nature of many of these acts, all of which have 
the appearance of being under the control of reason. For exam- 
ple, note the complicated nature of the process necessary to the 
successful deposition of the egg of the yucca moth {Promiba yiic- 
casclla). We are tokP that these moths emerge simultaneously 
with the flowers of the yucca, which open but for a single night 
and are practically dependent upon this particular moth for ferti- 
lization. When ready to oviposit, the female gathers a bundle of 
pollen from one flower, flies with it to another, pierces the tissues 
of the pistil of the latter, and lays her egg ; after which she 
ascends to the stigma of the same pistil and " stuffs the fertilizing 
pollen pellet into its funnel-shaped opening." 

Now this process is necessary not only to the fertilization of 
the yucca, but also to the grub that hatches from the egg^ which 
1 Morgan, Habit and Instinct, pp. 13-15. 



I06 VARIATION 

otherwise would be left without food. There is, therefore, a 
particular sequence in this complicated performance that must 
be observed or failure results ; and failure is fatal to the exist- 
ence of both species. 

Moreover, this act is performed but once in the lifetime of 
the moth, who has no knowledge of the acts of her predecessors, 
and is therefore not proceeding from simulation ; nor has she 
opportunity to learn the fate of her offspring and profit by 
the experience. 

Now the truth is that, unerring as is this performance, a 
good many ovules escape, from failure of the Qgg to hatch or 
from other causes, and thus the yucca is able to mature some 
seed. That complicated processes of this kind are not always 
carried out in proper sequence and full detail is shown by 
careful study of different individuals, as pointed out especially 
by Professor C. S. Crandall in his studies of the apple and plum 
curculio.^ 

Careful study of these complicated acts and of the body 
functions in general must convince the student not only of their 
nice adjustment but (what is of equal consequence) of their 
exceeding variability and irregularity within limits that certainly 
are by no means narrow. 

Cases of "double personality," in which the individual 
behaves for a time as another and distinctly different person, 
are too well known to require more than a passing notice. 
These are instances in which an entirely new set of functions 
is brought into play, — distinct from the normal, yet working 
together to the accomplishment of definite ends. 

But a few of the many modifications of normal functions 
have been mentioned. This is not the place to exhaust the 
subject. Only enough has been given to show the student that 
even the highly specialized functions are subject to the laws of 
variation. The matter will be more completely covered under 
" Causes of Variation." 

1 Bulletin AV. g8. Agricultural Experiment Station, University of Illinois, 
pp. 500-502. The account of the different ways in which three different females 
performed their work is given in full under " Transmission of Modifications," 
section on " Habit and Instinct." 



FUNCTIONAL VARIATION I07 

SECTION IV — NORMAL FUNCTIONS EXERCISED 
UNDER ABNORMAL CONDITIONS 

The mammary gland, normally confined to females, is com- 
monly functionless until after pregnancy ; but by manipulation 
of the udder, heifers and other females may be made to yield 
milk without bearing young. Again, rudimentary mammae, 
present generally in males, are occasionally accompanied by 
considerable development of mammary tissue, nearly always 
but not necessarily functionless.^ 

Most remarkable of all, mammary-gland tissue has been 
known to develop in extremely unusual places upon the body. 
Mammary tumors in the axilla (armpits) are described as of 
" common occurrence in lying-in women." ^ These tumors have 
no duct, but in squeezing they yield " both colostrum and 
milk," following in the same order as from normal mammae, 
and oozing through the skin " at the situations of the sebaceous 
follicles." 

Besides these there is " indisputable evidence of the presence 
of a mammary gland on the thigh . . ., on the cheek . . ., on 
the acromion (shoulder point) . . ., and in the labium majus. 
... In the two last cases the mammary nature of the gland 
was proved by microscopic examination." ^ 

Similar conditions may be produced artificially by grafting, 
and all sorts of abnormalities may testify to the persistence 
with which highly specialized tissue continues to discharge its 
functions, often under the most discouraging circumstances."* 

For example. Hunter and Duhamel grafted the spur of a 
young cock into his comb, " where it continued to grow to its 
normal size." ^ " Bert transplanted the tail of a white rat to 
the body of M?(s deciimanus (the common brown rat), where it 
continued alive." ^ The same experimenter bent over the tail 

1 Dr. Hottes, a personal friend of the writer, knew a young man in Germany 
who was suckHng an infant. 

2 Bateson, Materials, etc., p. 185. 

3 Ibid. p. 1S7. 

* As when a piece of mammary gland was grafted into the ear of a guinea pig ; 
when the pig became pregnant the gland commenced to secrete. 
^ Morgan, Regeneration, pp. 17S-179. 



I08 VARIATION 

of a rat and grafted it back into its own body. After it had 
united he severed it at the normal base and thus provided the 
animal with a " reversed tail." He found, however, that the 
tail of the mouse did not grow as well in the body of the rat and 
would not unite at all with the body of either the dog or the cat.^ 

Born succeeded in uniting the anterior and posterior parts of 
the tadpoles of two different genera of frogs {Rana csculcnta 
for anterior and Bombinator igneits for posterior). The combi- 
nation lived for ten days, when it was killed because of patho- 
logical changes. 2 

In the same way Harrison made up an individual of two 
species (Rana vircscens and Rana palnstris). This he kept alive 
until after its transformation into a frog, " each half retaining 
the characteristic features of the species to which it belongs." "^ 
This being true, it is not surprising that many varieties of 
apple can be grafted into the same tree top. Examples of this 
sort might be multiplied indefinitely, as in the making up of 
worms by grafting together pieces of two different species, in 
which each piece preserves its specific characters ; but enough 
has been given to show the persistence with which specialized 
tissue continues to discharge its natural function even under the 
hardest of conditions.^ 

The circumstances under which living matter can discharge 
its normal functions unaltered, either in character or in degree, 
and the limits beyond which these functions must cease or 
undergo alteration, — all this is not only a question of deep 
biological interest but it is one of special significance in breed- 
ing, because it throws no little light upon the real nature and 
causes of variability, a subject upon which we sorely need in- 
formation if variations are ever to be controlled either in their 
development or in their transmission. 

Summary. We are to regard variations in function as well 
as in form, of activities as well as of structure, of what an 
animal or plant does, as well as what it is. 

The body functions are not constant, but variable. They are 
variable as between different individuals and also with the same 

1 Morgan, Regeneration, pp. 178-179. ^ Ibid. pp. 183-185. 

^ Ibid. chap, ix, pp. 159-189, " Grafting and Regeneration." 



FUNCTIONAL VARIATION 109 

individuals at different times. They are variable not only in 
degree but also in kind, and normal functions may be disturbed, 
even altered, by external influences. Conversely, usual func- 
tions may be discharged under most unusual conditions. 

All variation is either continuous or discontinuous, and contin- 
uity must not be assumed. Many of the fundamental qualities 
of living matter, such as definite composition, argue for discon- 
tinuity. 

ADDITIONAL REFERENCES 

Immunity and Adaptation. Biological Bulletin, IX, 141-151. 
Geldings more Susceptible to Disease than Mares. Experiment 

Station Record, XI, 896. 
Variation in Immunity to Anthrax (among sheep). By Martinet. 

Experiment Station Record, XIII, 186. 
Insectivorous Plants. By Charles Darwin. 

For good evidence on functional variation consult the speed records 
of trotting and running horses and the Advanced Registry of Jersey and 
Holstein-Friesian Cattle. 



CHAPTER VI 

MUTATIONS 

SECTION I — DISTINCTION BETWEEN MUTATION 
AND ORDINARY VARIATION 

The deviations from type heretofore considered are those of 
individuals rather than of groups. Whether quantitative, sub- 
stantive, meristic, or functional, they represent the fluctuations 
of individual members of a species or a variety about the nor- 
mal type of the race, not necessarily exhibiting any tendency 
to depart permanently from that type. 

The study of these deviations shows that, while no two 
individuals are alike, yet the departures of certain individuals 
in one direction are compensated by departures of other indi- 
viduals in the opposite direction. In other words, the members 
of a race cluster closely about what may be called a center of 
fluctuation, which is, in most cases, comparatively stationary. 
Because of this fact we may have a relatively fixed type, 
indicating a practically stationary race, even in the midst of 
considerable individual deviation.^ 

Mutations, on the other hand, mark sudden and distinct 
departures from type. The pendulum swings, but does not re- 
turn. A new center of fluctuation is established, from which 
individuals deviate in all directions as before. It is not that 
the old center is abandoned, — for the mass of individuals still 
cluster about it as before, — but it is that a new center is estab- 
lished, about which a new group clusters, and all close observers 
recognize at once that a new type has been born into the world 

1 This fact is extremely confusing, especially to animal breeders. In the midst 
of wide variations and with but few individuals living at any one time, the breeder 
is often unable to tell whether his general average (or type) is improving, retro- 
grading, or standing still. This matter will be alluded to again under " Type and 
Variability." 



MUTATIONS 1 1 1 

and a new race is established on the earth. This new group 
and its center constitute a mutation, and the individuals are 
spoken of as mutants. Variation has become discontinuous as 
well as continuous. 

These sudden offshoots from established species were noted 
by Darwin, who called them sports. He considered, however, 
that new species are formed only by the slow but continuous 
action of selection working with ordinary fluctuations (continuous 
variations), building up new types a little at a time through the 
gradual accumulation of slight but favorable deviations. 

His so-called "sports " were therefore mysterious, and from 
the fact that under natural conditions they generally disappear 
rapidly by crossing, he was led to attach little importance to 
these sudden departures from the established type.^ Later 
researches, however, have given them unexpected significance. 

The distinguishing feature of a mutation is that there are no 
intermediates between the old type and the new, which was 
therefore attained not by slow degrees but by a sudden leap ; 
that there is but a slight tendency to revert to the old form, 
but that if reversion takes place at all it is complete at once and 
the return is to the old type and not to an intermediate form. 
The mutant is distinctly a case of discontinuity. 

SECTION II — EXAMPLES OF MUTATION 

The classic examples of mutation are the weeping willow and 
the nectarine. They are to be regarded, however, as familiar 
illustrations of general principles widely operative and giving 
rise not to few but to many distinct types. 

When a seed germinates it puts out two sprouts. One is 
positively geotropic ; that is, it responds to the force of gravity 
and grows downward into the soil, developing the root system. 
The other is negatively geotropic ; that is, it grows upward 

1 The student of evolution should gain the conception that the type of a race 
is not a fixed point from which deviations radiate ; it is rather the center of 
gravity of all the individuals of the race, its exact location depending upon the 
extent and direction of individual deviations, shifting slightly from time to time 
with the causes that influence variability. 



I I 2 VARIATION 

against gravity, and with an energy sufficient to maintain it in 
a fairly upright position, developing stems, branches, and leaves. 

Occasionally this latter geotropism fails, and the branches 
hang downward, forming a "weeping" variety. This is espe- 
cially common in the willow and the birch, though by no means 
unknown in other trees, notably the elm, maple, and beech. 

"Cut-leaved" varieties and "fan tops " ^ occasionally arise 
suddenly, all of which may be preserved by grafting or by bud- 
ding, so that with proper attention we may have weeping, cut- 
leaved, and fan-top varieties, not of a few but of many species 
of trees and shrubs, although the readiness with which a partic- 
ular mutation may appear in one species is no guaranty of its 
appearance in another. 

A tree which has always before borne peaches may suddenly 
bear nectarines, or more likely a single branch may make the 
departure, the remainder of the tree continuing to bear peaches 
as before. In any event the mutation may be propagated by bud 
or possibly by seed, — in which latter case a nectarine-bearing 
tree results. This tree may bear nectarines all its life, or it may 
occasionally bear peaches on the whole or a portion of its top. 
The significant fact is that there is no intermediate between the 
peach and the nectarine, and yet the one may arise at any time 
from the other.^ The mutation from peach to nectarine is clear- 
cut and distinct, and the reversion from nectarine to peach 
when it occurs is equally complete. 

The apricot appears to be related to the plum much as 
the nectarine is to the peach. In both cases the main stocks 
(peaches and plums) exist in many varieties, and the mutations 
(nectarines and apricots) in but few. In the case of the former 
(the peach) the main stock is downy, while the mutant is gla- 
brous, or destitute of downy covering. In the latter, however, 
the conditions are reversed, for the main stock (the plum) is 
glabrous, while it is the mutant that is downy. 

1 A fan-top tree is one in wiiich the branches are borne on opposite sides, after 
the fashion of corn. In a small forest plantation belonging to the writer is a fan- 
top linden, now grown to considerable proportions. 

■^ Inasmuch as the peach is considered as the main race, the nectarine is said 
to arise from the peach by mutation. Therefore when peaches are borne upon 
nectarine trees the case is considered to be one of reversion. 



MUTATIONS 1 1 3 

Because the apricot has never been observed to arise direct 
from the phim as the nectarine has repeatedly been known to arise 
from the peach, and because the apricot trees have never been 
known to bear plums as the nectarine trees occasionally bear 
peaches, — because of these facts botanists have quite generally 
ceased to regard the apricot as a sport from the plum, and are 
agreed, I believe, in considering it as a distinct species. 

However, it behaves precisely like a mutant, and in consider- 
ing the means by which new types originate the presumptive 
evidence is strong that the apricot originally sprang from the 
plum stock. Though it is true that some mutations are fre- 
quently repeated, it is also true that others arise but rarely. 
The nectarine is unusual in the frequency with which it reap- 
pears, and the readiness with which the peach and its mutant 
exchange places has perhaps no parallel. 

In many respects the apricot appears like an intermediate 
between the peach and the plum. The external appearance of 
the fruit is that of the peach. The pit is smooth, resembling 
that of the plum. The bark of the tree is like that of the peach, 
but the leaf is like that of the plum. There is nothing to sug- 
gest a hybrid origin, though everything to suggest that this 
strange plant and its fruit are in some way composed of the 
elements of both the peach and the plum. 

Nor would a hybrid origin be at all necessary to this fact. 
Certain characters are general, running through many species 
quite independent of consanguinity. Thus the weeping or the 
cut-leaved habit is common to a great variety of species only 
remotely related. The downy character is common with both 
fruit and leaf, and almost every downy or pubescent species has 
its glabrous or smooth variety, — its mutant in all probability, 
and one that easily and frequently arises. So also, without 
doubt, the reverse is true by which smooth species occasionally 
throw off downy or pubescent varieties. Now this particular 
character of pubescence, while simple enough in itself, is yet 
exceedingly noticeable, and serves to insure a specific name, 
unless indeed the direct origin happens to be extremely well 
known, in which case the mutant is likely to get off with a 
varietal distinction. 



114 



VARIATION 



In the same general manner, color is likely to fail, and nothing 
is more common in nature than albino varieties. Thus we have 
our white currant, strawberry, raspberry, and even the black- 
berry, — almost every thicket affording its examples and speak- 
ing eloquently of the freedom with which nature creates new 
forms, and if we will only open our eyes to see what is going on 
about us, we shall learn much of how it is done. 

Albinism among animals is even more common than among 
plants. Men, dogs, cats, horses, cattle, sheep, bears, rabbits, 
rats, mice, and many other species are distinguished by albino 
varieties. 

These distinctions, marked though they are, arise doubtless 
from the simplest causes. For example, if an animal for any 
reason fails to secrete pigment in the normal manner it is from 
necessity an albino, and if the failure is hereditary an albino 
race is likely to be established, although unrestricted breeding 
greatly reduces its probability through crossing with other forms. 

SECTION III — EXPERIMENTS OF DE VRIES i 

Hugo De Vries, professor of botany in the University of 
Amsterdam, long ago became convinced that Darwin's theory 
of the origin of species through the gradual accumulation of 
fortuitous variations is not the only means of creating new types. 
Darwin taught not only that existing types had been preserved 
by selection because they in some way fitted the conditions of 
life, but that the intervening spaces between species and varieties 
represent extinctions through the agency of natural selection. 

De Vries came to believe that, in many cases at least, the new 
type springs suddenly from the old, without gradation and without 
intervening forms, and that while selection may shape up the 
new type and perhaps the better fit it for existence, yet the 
selective process is in no way responsible for its origin. Indeed, 
one of the earliest evidences, to his mind, that new types often 
arise without the agency of selection, was the notable fact that 
new forms arising spontaneously in nature are for the most 

1 Hugo De Vries, Species and Varieties, their Origin by Mutation [Open Court 
Publisliing Company, Chicago]. 



MUTATIONS 115 

part promptly exterminated by the rigors of natural selection, 
which therefore could not have been the chief agency in their 
creation. 

Accordingly he conceived the idea of cultivating a few unstable 
forms under conditions such as would protect and preserve any 
mutations that might arise, hoping in this way to throw some 
light on the origin of new types and to determine whether in the 
origin of species natural selection works principally upon indi- 
viduals or upon types. 

Experiments with toadflax ^ (Linaria vulgaris) . These experi- 
ments were designed to test the origin of the peloric form.^ The 
toadflax was chosen, first because the peloric form is known to 
have arisen repeatedly, and second because the change involved 
is slight, structurally speaking. These two considerations gave 
reason for the hope that if the species were put under careful 
observation and control, he (De Vries) "might be present at the 
time when nature produces another of these rare changes." 

The experiments commenced in 1886 with normal plants bear- 
ing "one or two peloric flowers," as is common with most indi- 
viduals of this genus. The roots were planted in the garden, 
and flowered and seeded in 1887. This second generation was 
grown for three years, producing in 1889^ one, and in 1890 two, 
peloric structures. The seeds of these were saved and produced 
the third generation in 1890— 189 1. Among some thousands of 
blossoms in this generation there was one five-spurred flower. 
This was pollinated by hand and luckily produced "abundant 
fruit, with enough seeds for the entire culture of 1892, and they 
only were sown." * 

1 De Vries, Species and Varieties, etc., pp. 464-487. 

2 The normal flowers of the toadflax are exceedingly unsymmetrical. Aside 
from bearing a short spur, they are described as consisting of a " two-lipped corolla, 
the lower lips spreading and three-lobed, with a base so enlarged as to nearly 
close the throat." Plants bearing such unsymmetrical flowers as do toadflax, snap- 
dragon, etc., are known occasionally to produce peloric, that is, symmetrical, 
flowers. Not only that, but peloric varieties are not unknow^n, and these experi- 
ments were designed to solve the manner of their origin. 

3 The toadflax is a biennial. 

* Peloric flowers of this species are commonly sterile, but in any case are 
dependent upon artificial fertilization. They are by nature ill adapted to preserve 
themselves. 



Il6 VARIATION 

Up to this point in the experiment each generation required 
two years, as the toadflax is a biennial, not blooming until the 
second year. After this, however, the seedlings were started 
under glass and transplanted to the garden in June. By this 
means the new plants were made to produce flowers and seeds 
the first year. 

About twenty plants of this (fourth) generation were secured, 
and under this treatment most of them produced seed the first 
year. Only one peloric flower was observed, however, in the 
entire lot. The plant bearing this flower and one other were 
preserved, and all others were destroyed. These two fertilized 
each other freely and produced lo cc. of seed, but no more 
peloric flowers appeared. It is from this pair of plants, how- 
ever, that a peloric race finally sprung.^ 

In 1894 about fifty plants were in flower. There was no rea- 
son for considering these plants any more promising than pre- 
vious sowings, except that " stray peloric flowers were observed 
in somewhat larger numbers than in previous generations, — 
eleven plants bearing one or two, or even three, such abnor- 
malities." De Vries wisely remarks that this "could not be 
considered as a real advance, since such plants may occur in 
varying though ordinarily small numbers in every generation." 

However, besides these eleven individuals, each bearing one 
or two abnormal flowers, tJicre ivas a single plant bearing only 
peloric flozuers. The mutation had arisen and De Vries "was 
present at the time." 

This plant was carefully kept, all others being destroyed, and 
the next year it bloomed again, bearing only peloric flowers. It 
was true to its type. In this connection De Vries says : 

Here we have the first experimental mutation of a nonnal into a peloric 
race. Two facts were clear and simple : [first] the ancestry was known 

1 It has been said that the flowers of one plant are sterile to pollen from the 
same plant. De Vries ascertained by careful experiment that this is true in about 
50 per cent of the cases, so that, though a much higher degree of fertility exists 
between individuals than within the individual, absolute barrenness between all 
flowers of the same plant cannot be asserted. The point is not significant in the 
present connection, but it is important as demonstrating that fertility and sterility 
are not always in direct proportion to consanguinity, and that, though close breed- 
ing may be commonly infertile in certain strains, it by no means follows that it is 
always infertile even in the same strain. 



MUTATIONS 117 

for over a period of four generations. . . . This ancestry was quite constant 
as to the peloric peculiarit}', remaining true to the wild type as it occurs 
everywhere in any country, and showing in no respect any tendency to the 
production of a new variety. 

[Second] the mutation took place at once. It was a sudden leap from 
the normal plants with very rare peloric flowers to a type exclusively peloric. 
The parents themselves had borne thousands of flowers during two summers, 
and these were inspected nearly every day in the hope of finding some pelorics 
and of saving their seed separately. Only one such flower was seen. . . . 
There was simply no visible preparation for this sudden leap. 

This leap on the other hand was full and complete. No reminiscence of 
the former condition remained. Not a single flower on the mutated plant 
reverted to the previous type. . . . The whole plant departed absolutely 
from the old type of its progenitors. 

The next object was to seek for other mutants from the same 
lot of seed ^ and to compare their proportion with the proportion 
coming true from the seed of the first mutant. 

Accordingly De Vries planted his entire remaining stock of 
seed, which, it will be remembered, was grown from the pair of 
plants one of which bore a single peloric flower, but both of which 
were immediately descended from the single five-spurred flower 
of the third generation. 

From this seed he grew about two thousand plants in well- 
manured soil. About 1750 of these bore flowers, and among 
these sixteen, or about i per cent, were wholly peloric. As these 
seeds were of the same generation that produced the first mutant, 
he concludes that the chance of a peloric mutant is not over one 
in a hundred. 

De Vries next undertook to determine whether the mutation 
would be repeated in another generation, for up to this point all 
the mutants had arisen from the same lot of seed. For this 
purpose he saved seeds from normal plants so isolated as to pre- 
vent crossing with peloric strains. In one instance he " obtained 
two and in another one peloric plant with exclusively many- 
spurred flowers," showing conclusively that mutations are itera- 
tive, and that the same conditions that produce one mutant 
will from time to time produce others altogether similar. 

1 It will be remembered that the original stock of seed of this generation was 
ID cc, but that only enough had been grown to produce fifty plants, leaving a 
quantity still on hand. 



Il8 VARIATION 

New type persistent. Next he undertook to determine to what 
extent these mutant pelorics would " breed true," in order to 
compare the proportion with the previously ascertained i per 
cent. In this he encountered difficulty because of the high 
degree of sterility of peloric flowers. He had in all some twenty 
plants, and pollinated artificially more than a thousand flowers. 
Of these he says : 

Not a single one gave a normal fruit, but some small and rudimentary 
capsules were produced bearing a few seeds. From these I had 1 19 flower- 
ing plants, out of which 106 were peloric and the remainder (13) one-.spurred. 
The great majority (some 90 per cent) were thus shown to be true to their 
new type. Whether the 10 per cent reverting ones were truly atavists caused 
by stray pollen grains from another culture cannot of course be detemiined 
with sufficient certitude. 

This experiment determines not only the distinctness of the 
new type and the suddenness of its formation, but its essential 
purity as well ; for it bred true in 90 per cent of the cases, while 
the probability of original mutation was slight, certainly not over 
I per cent. 

The total lack of intermediate steps in the control experi- 
ments is significant. Their absence in nature is not less so (for 
if they were present as transition steps toward the formation of 
peloric races, they would certainly be discovered, particularly 
when we remember that the species is a perennial), and the con- 
clusion seems inevitable that the transition is abrupt, and the 
new type, repeatedly re-formed, is without doubt to be regarded 
as a true mutation. 

The common snapdragon, whose flowers are exceedingly un- 
symmetrical, also has a peloric race. " But the snapdragon is 
self -fertile, and so is its peloric variety," observes De Vries. 
These mutations are therefore much more easily preserved, and 
are, as we should expect, more common than in the toadflax, — 
so common and so distinct as, without a doubt, to give rise to 
real hybrids with the old form. 

What is true of toadflax and snapdragon is held to be true of 
unsymmetrical flowers generally ; namely, a strong tendency to 
give rise from time to time to peloric varieties, not by gradual 
change of the parent stock but by sudden offset, or mutation. 



MUTATIONS I 1 9 

Experiments in the production of double flowers. ^ After 
remarking that mutations occur as often among cultivated as 
among wild plants, De Vries drops the caution that in all experi- 
mentation of this order hybridism must be carefully guarded 
against.'^ He observes, too, that white varieties seem compara- 
tively old, as they are common in the wild state, while double 
flowers are rare in the wild state and correspondingly recent, 
indicating their origin under cultivation, and thus making the 
matter of doubling a favorable character with which to conduct 
investigations upon mutation. 

In the experiments upon peloric toadflax nothing new was 
attempted. The object was to repeat what nature was known 
often to have done, but so to control conditions as to " be there " 
when it happened next time. 

In this experiment, however, De Vries determined to attempt 
a new mutation, — that is, to try to secure double flowers where 
they had never been observed in nature. He accordingly chose 
the corn marigold (ClirysantJievmvi scget?im), common in the 
grain fields of central Europe, and its cultivated variety, grandi- 
Jioniin. The number of ray florets is variable in both, but is, 
on an average, thirteen in the wild and twenty-one in the culti- 
vated. This indicated the latter as the more favorable for the 
experiment, and it was therefore chosen; but it is far from pure, 
for many of its heads have as few as thirteen rays. Only six 
out of the first lot of three hundred plants reached an average 
of twenty-one, and these were selected as the foundation. 

The seeds of each of these were sown separately. Five gave 
proof of being still mixtures with the wild form and were re- 
jected. The offspring of the sixth plant averaged twenty-one 
ray florets, and after counting some fifteen hundred heads the 
two plants were selected whose secondary heads made the best 
showing. The progeny of these plants also averaged twenty-one, 

1 De Vries, Species and Varieties, etc., pp. 489-515. 

2 If a new form is a mutant it will " breed true " to itself in the great majority 
of cases and perforce hybridize with the original stock. If, on the other hand, it 
is an ordinary hybrid, it will not breed true, but will observe the principle of 
Mendel's law (to be discussed later), by which a certain definite percentage is of the 
original types. Thus it is comparatively easy to ascertain whether a new type is the 
product of a single race by mutation or of two races by hybridization. 



1 20 VARIATION 

and De Vries considered that the strahi was now pure and that 
" no further selection could be of any avail." 

One of these two plants was distinguished by producing two 
secondary heads with tiveiity-tivo rays, whereas generally only 
the terminal head reached so many as tzventy-one, the other 
retrograding often as low as to thirteen. This exceptional plant 
was distinguished only by these two secondary heads. Its ter- 
minal head had but twenty-one rays, and the average of all its 
heads was not exceptionally high ; but no other plant out of 
hundreds had ever produced secondary heads with more than 
twenty-one rays, and it was from this plant that the double- 
flowering line developed three years later. 

This plant appeared in 1896. Its seed was sown in 1897. 
The largest number of rays in the terminal head suddenly 
increased from twenty-one to thirty-four; next year (1898), to 
forty-eight ; next (1899), to sixty -six ; and during this time the 
general average for all the heads increased remarkably. No 
indication of doubling had, however, yet appeared. The im- 
provement was such as follows selective breeding with fluctuat- 
ing variability, — improvement by gradual change and without 
mutations. 

Late in the season (September) of this year (1899), how- 
ever, three secondary heads appeared on one plant with a few 
ray florets scattered over the disk. The mutation anxiously 
awaited for seven years had suddenly appeared in this small, 
belated way toward the close of the growing season, and in 
a manner that would have escaped the attention of any but 
the most painstaking investigator,^ and that would have invited 
extermination in nature. 

This was in 1899. The heads were of course pollinated with 
other and inferior flowers, but in 1900 the highest number of 
rays rose to one hundred, and in 190 1 reached two hundred. 
He remarks, " Such heads are as completely double as are 

1 The student will note that every flower of thousands of plants was carefully 
examined, and that in every case the foundation of the mutation was in an incon- 
spicuous plant, certain to be overlooked by casual observers. The obvious lesson 
is that only the most careful and systematic examination will detect the founda- 
tion stock, so easily does it escape notice in the general mass and so readily is it 
lost unless isolated and protected. 



MUTATIONS 121 

the brightest heads of the most beautiful double commercial 
varieties of composites." He adds : 

The race has at once become permanent and constant. Real atavists or 
real reversionists were seen no more after the first purification of the race. 
It has of course a wide range of fluctuating variability (considering all 
the heads), but the lower limit has been worked up to about thirty-four 
rays, a figure never reached by the grandijlonnn parent, from which my 
new variety is sharply separated. 

Unfortunately, the best heads now produced are sterile, so 
that seeds must be secured from inferior stock and the variety 
must be propagated from slightly inferior parentage. Selection 
has, therefore, reached its limit, unless a fertile strain arises, 
which is entirely possible. 

This mutation is decidedly new. It had never been known, 
nor had anything approaching it ever been discovered in this 
species. The only hope that it might appear was belief in the 
principle, and the fact that doubling had taken place in other 
compositae. Right royally was De Vries's prophecy fulfilled, and 
again was he " present " when it happened ; not only that, but 
in this case nature evidently would not have produced this 
mutation without assistance. Here nature has accomplished 
with help a work which she was powerless to accomplish alone, 
but abundantly able to achieve with a little assistance. 

Experiments in the production of new species.^ De Vries was 
not content with the simple production of varieties. He desired 
to show that the principle of mutation produces species as well.^ 
He cultivated many species of wild plants in his garden, choos- 
ing wild in preference to cultivated, because he regarded the 
latter as evidence of what had recently taken place and, there- 
fore, not the best stock for further mutation in the near future. 
In other words, he desired to be present before the mutation 

1 De Vries, Species and Varieties, etc., ])p. 516-546. 

2 He distinguishes sharply between varieties and species. The variety differs 
from the main stock in but a single character, progressive or retrogressive, while 
the species differs in all characters, some of which are perhaps progressive and 
others retrogressive. He likes to distinguish elementary species from all other 
types, as these are in his estimation the most stable forms in nature ; and when 
any race assumes the " mutative state " it is likely to throw off, if conditions are 
favorable, a large number of new elementary species, each with its new center of 
variability. 



122 VARIATION 

happened, rather than to enter just afterward and only in time 
to note results with no evidence as to methods. 

Of all the hundreds of plants cultivated he foimd the evening 
primrose most fertile in distinct strains, both in the wild and 
in the cultivated state. Other species gave rise to varieties 
freely, but no other appeared to be sufficiently mutable to give 
rise freely to what he regarded as elementary species. 

Of all the primroses, GinotJicra Laviarckiana, commonly called 
Lamarck's evening primrose, was the most prolific in distinct 
forms, and accordingly this was chosen by De Vries for special 
attention in his experiments. It is described as "a stately 
plant with a stout stem, attaining often a height of 1.6 m. or 
more. When not crowded, the main stem is surrounded by a 
large circle of smaller branches growing upward from its base 
so as to form a dense bush. These branches in their turn have 
numerous lateral branches. . . . Contrary to their congeners, 
they are dependent on visiting insects for pollination." 

Ordinarily this primrose is a biennial, producing rosettes in 
the first year and stems in the second year. Both the rosettes 
and the stems are highly variable in nature, producing a num- 
ber of distinct races, some of which show a marked ability to 
hold their own under natural surroundings, while others are too 
weak to endure. 

Many of these De Vries regarded as new species. Experi- 
ments to determine this point were commenced with stock dis- 
covered near Hilversum, and three plans were followed : first, to 
transplant the apparent new species into the garden whenever 
the new race was sufficiently strong; second, to reproduce weak 
races by sowing seeds from "indifferent" plants growing wild ; 
third, to sow the seeds from the introduced plants. " These 
various methods," he adds, "have led to the discovery of over 
a dozen new types never previously observed or described." 

These new plants are divisible, according to De Vries, into 
five different heads or " groups " : (i) those that " are evidently 
to be considered as varieties in the narroivcr sense of the 
word," representing retrograde development ; (2) " progressive 
elementary species" which are "as strong as the parent 
species " ; (3) " progressive elementary species," but weaker than 



MUTATIONS 



123 



the parent, and "apparently not destined to be successful"; 
(4) certain forms that are "organically incomplete"; (5) "in- 
constant forms." 

Group (i), retrograde varieties. Of this class the following 
three forms were discovered, all produced in nature as well as 
in the garden : 

O. Icevifolia, the smooth-leaved variety, constant from seed and 
never reverting except from crossing. As strong and fertile as 
the parent. 

O. brcvistylis, the short-styled form. In this the ovary is so 
placed that it is reached by very few pollen tubes. Thus while 
the plant is vigorous it is but indifferently productive of seeds, 
and as De Vries says "many [capsules] contained no seeds at 
all ; from others I have succeeded in saving only a hundred seeds 
from thousands of capsules." These seeds, however, reproduce 
the variety without reversions to Lamatxkiana. 

O. nanella, the dwarf, "a most attractive little plant, . . . 
very short of stature, reaching often a height of only 20-30 cm., 
or less than one fourth of that of the parent." The flowers 
are as large as those of the parent ; the leaves are much 
smaller and with no reversion in seedlings, even in repeated 
and successive generations. 

Group (2), progressive elementary species, and vigorous ; two 
forms discovered : 

O. gigas, the giant, deserving its name not from being higher 
than its parent, but because it is " so much stouter in all 
respects." The stems are often twice as thick as in the parent 
{Lamarckiana), and the " internodes are shorter and the leaves 
more numerous, covering the stems with a denser foliage." The 
flowers are larger, and the seed capsules are smaller and filled 
with fewer but larger seeds than in the parent plant. It has a 
strong tendency to remain a biennial. 

O. rnbrinei'vis, the red-veined form. In this the veins of the 
leaves are distinctly tinged with red and the fruits are streaked 
with red. The plants are in many ways a counterpart of the 
giant, except for the red tinge and distinctly lighter foliage. 
This latter probably accounts for the marked tendency on the 
part of this form to become an annual. Like the giant, this form 



124 



VARIATION 



is true to type when grown from the seed, and its recurrence is 
far more common than is that of gigas, which is extremely rare. 

Group (3), progressive elementary species, but weakly. Two 
forms : 

O. albida, the albino, with whitish, narrow leaves, "appar- 
ently incapable of producing sufficient quantities of organic 
food." The seedlings are exceedingly delicate, and if left to 
themselves will be speedily overgrown by their more vigorous 
neighbors ; but if transplanted and given the best of care, they 
make fairly vigorous plants the second year, comparing fairly 
well with the parent stock but bearing fewer seeds. They 
come true even to the third generation and the type remains 
distinct. 

O. oblonga, the narrow-leaved form. It " may be grown either 
as an annual or a biennial. In the first case it is very slender 
and weak, bearing only small fruits and few seeds. In the alter- 
native case, however (biennial), it becomes densely branched, 
bearing flowers on quite a number of racemes and yielding a 
full harvest of seeds." 

The investigator says : 

We have now given the description of seven new forms which diverge 
in different ways from the parent type. All were absolutely constant from 
seed. Hundreds or thousands of seedlings may have arisen, but they 
always come true and never revert to the original O. Lainarckiaiia. 

He adds the remark that they have inherited the condition of 
mutability to some extent and are evidently themselves able to 
produce new forms, but that they do so but rarely. 

Two other forms belong to this group, — O. semilata and 
O. leptocarpa, — but their characters do not merit special 
description. 

Group (4), forms organically incomplete : 

O. lata is a pistillate variety, wholly dependent for fertiliza- 
tion upon other forms, and it had therefore no opportunity to 
establish its type, which, however, freely appeared. It is a "low 
plant," but with "dense foliage and luxuriant growth." Its 
presence can be detected in the seedling by the " broad, sinuate 
leaves with rounded ^ tips." Being pistillate, it produces seed 
only when cross pollinated, in which case its characters are 



MUTATIONS 



125 



transmitted to a portion only of its offspring, thus behaving hke 
hybrids. Indeed, he specifies that " on the average one fourth 
of the offspring are lata," the others assuming the character of 
the pollen parent," — a strict example of hybridism between a 
weaker and a stronger form, according to Mendel's law. 

Group (5), inconstant forms : 

O. scintillans is a perfectly fertile form, bearing smooth, dark- 
green leaves with glistening surfaces. It is a natural dwarf, 
easily cultivated as an annual. When fertilized with its own 
pollen to produce a " pure " strain, it is found that the seedlings 
all resemble the parent, but that soon afterward they diverge 
into various types. Some of these resemble the original parent 
stock {Laniai'ckiana) and others remain pure, but the proportion 
is very variable. These might be regarded as simple reversions, 
except that occasionally other types appear, especially oblonga, 
lata, and nanella, the first often constituting 10 per cent of the 
sowings. It thus shows a disposition to give rise to the same 
distinct forms as does its own parent, and is thus regarded by 
De Vries as being itself in a " highly mutable state." 

O. clliptica is a narrow-leaved, inconstant type, exceedingly 
"difficult of cultivation." Though fertile to its own pollen, it 
" repeats its type only in a very small proportion of its seeds." 

There are thus " a dozen new types springing from an original 
form in one restricted locality and seen to grow there, or arising 
in the garden from seeds collected from the original locality." 
Most of these types behave with a constancy that ranks them, 
for breeding purposes at least, as distinct forms, good elementary 
species, — new things in the earth that may be held constant or 
that may be slightly modified by the exercise of selection among 
the fluctuations to which all types both old and new are subject. 
The experimenter observes : 

It is most striking that the various mutations of the evening primrose 
display a great degree of regularit}-. There is no chaos of forms, no indefi- 
nite varying in all degrees and in all directions. On the contrary', it is at 
once evident that very simple rules govern the whole phenomena. 

History of the experiment. In all De Vries made four differ- 
ent series of pedigree cultures of the evening primrose, extend- 
ing from five to nine generations and including thousands of 



126 VARIATION 

plants. The types that arose at different times have already 
been described, but considerable interest and no Httle profit 
attaches to the details of the experiment, especially in re- 
gard to the order and manner of the appearance of the new 
types. The following is abstracted from the experimenter's 
account of one of these four experiments, running through 
eight generations.^ 

Beginning in the fall of 1886 he took nine large rosettes of 
O. Lamarckiana from the field and planted them in the garden. 
The second generation was sown in 1888 and flowered in 1889. 
The seed produced fifteen thousand seedlings, of which ten 
were divergent at once, — five lata and five nanella. No inter- 
mediates appeared. "They came into existence at once," says 
De Vries, "fully equipped, without preparation or intermediate 
steps. No series of generations, no selection, no struggle for 
selection was needed. It was a sudden leap into another type, 
— a sport in the best acceptation of the word." ^ 

The third generation of ten thousand plants showed three lata 
and three nanella, besides one riibrinervis. 

Growing expert in detecting mutants at an early stage, he 
discovered 334 young plants out of 14,000 of the fourth gener- 
ation (1895). This is about 2.5 per cent. Of these 176 were 
oblonga, 73 lata, 60 nanella, 15 albida, 8 riibrinervis, i scintil- 
lans, and i gigas. 

The larger number and wider range of mutants discovered 
this year are to be ascribed to growing skill in detecting them 
at an early age. Manifestly such immense numbers must be 
greatly reduced at the earliest possible date, and without doubt 
some good forms were overlooked in the earlier generations. 
After this (fourth) generation the number of seedlings was 
greatly reduced, with the effect of reducing the number of 
mutants and also the chances of the rarer forms appearing at 
all ; indeed, ^z>^?j- never appeared again, and scintillans not after 

1 De Vries, Species and Varieties, etc., pp. 549-556. 

2 It may occur to the student to object to the conclusion on the ground that 
the parent stock taken from the field may not itself have been pure. If, however, 
the stock had been in any sense hybrid, the departures should have been, accord- 
ing to Mendel's law, more than ten ; but not in this or in later generations did 
either parent stock or mutant behave like a hybrid in this respect. 



MUTATIONS 



127 



the sixth generation. The entire results of the eight generations 
of breeding are given in the following table. 

Eight Generations of a Mutating Strain of Evening Primrose 
(^O. Lamarckiana) 





Genera- 
tions 


0. 
gigas 


Albida 


OMonga 


Rjibri- 
nervis 


Lamarck- 
iana 


Natiella 


Lata 


Scintil- 
latis 


I 










9 








II 










15,000 


5 


5 




III 








I 


10,000 


3 


3 




IV 


I 


15 


176 


8 


14,000 


60 


73 


1 


V 




25 


135 


20 


8,000 


49 


142 


6 


VI 




I I 


29 


3 


1,800 


9 


5 


I 


VII 






9 




3,000 


II 






VIII 




5 


I 




1,700 


21 


I 





In the opinion of the experimenter here are numbers enough 
and types suflficiently distinct to warrant the enumeration of 
certain laws or principles that appear to govern the appearance 
of mutants, especially in the species under observation. This 
De Vries attempts to do, but without presuming to say how 
closely they may apply to other strains of plants or animals. 

Laws of mutability for evening primroses. De Vries' experi- 
ments. On the basis of his experiments with the evening prim- 
rose the investigator announces the following laws of mutability 
as applying to that species :^ 

1. "That new elementary species appear suddenly, without 
intermediate steps." As proof he points out that no interme- 
diate forms appeared to fill the gaps, and that no selection was 
necessary to establish the type. 

2. "New forms spring laterally from the main stem." " The 
current conception concerning the origin of species (or new 
forms generally) assumes that species are slowly converted into 
others. The conversion is assumed to affect all the individuals 
in the same direction and in the same degree. . . . The birth 

1 De Vries, Species and Varieties, etc., pp. 558-575. These laws, while 
announced for the evening primrose, are without doubt of wide if not general 
application. 



128 VARIATION 

of a new species necessarily seemed to involve the death of the 
old one," at least the old merged into the new. 

The experimenter points out, however, that through all the 
process of originating a dozen or more distinct forms, the parent 
stock continued unchanged, and still constituted the principal 
strain of all the primroses,^ and from this he deduces the law 
that mutants are laterals. 

3. " New elementary species attain their full constancy at 
once." " Constancy is not the result of selection or of improve- 
ment. It is a quality of its own. It can neither be constrained 
by selection if it is absent from the beginning, nor does it need 
any natural or artificial aid if it is present." 

De Vries remarks that scintillans repeats its characters in 
but part of its offspring, and that he has " tried to deliver it 
from this incompleteness of heredity but in vain. . . . The insta- 
bility seems to be here as permanent a quality as the stability 
in other instances. Even here no selection has been adequate 
to change the original form." He regards it as itself in a state 
of instability. 

4. " Some of the new strains are evidently elementary species, 
while others are to be considered as varieties." 

Elementary species are regarded as possessed of progressive 
characters, but varieties as differing from their parent stock in 
but a single character, and that in the way either of an assump- 
tion or of a loss. The elementary species is, therefore, a new 
aggregation of characters, while the variety is simply the old 
form minus a single character. Whether this distinction holds, 
remains to be determined. Much of the argument turns upon 
what is to be considered as a character and when it is lost. For 

^ A natural corollary to this observation is to remark upon the erroneous popu- 
lar assumption that of similar and contemporaneous forms the more primitive are 
necessarily the progenitors of the more nearly perfect. For example, it is hastily 
assumed that if evolution is true then man must be the direct descendant of the 
ape. But the ape, though very old, is still an ape, and he is not descending into 
anything but apes. Though evidently developed from the same original stock at 
some time and in some way, whether by one or by many mutations nobody knows, 
yet the gap between us is evidently fixed and not growing less or being bridged 
at any point. Good evolution regards related forms as connected by ties of con- 
sanguinity, but whether direct, or, what is more likely, indirect, running to some 
extinct common ancestor, only a novice will attempt to say. 



MUTATIONS 129 

example, is the smooth leaf or stem considered as having lost a 
character as compared with its downy relative ? 

5. '* The same new species are repeatedly produced," that is 
to say, the same new forms arise again and again, showing that 
the tendency to their production is inherent and persistent. 
" This is a very curious fact," remarks De Vries. " It embraces 
two minor points, — the multitude of similar mutants in the 
same year, and the repetition thereof in succeeding generations. 
Obviously there must be some common cause. This cause must 
be assumed to lie dormant in the Lamarckians of my strain, etc. 
. . . The germs of the oblonga, lata, and nanella are very irritable 
and are ready to spring into existence at the least summons, while 
those of gigas, rubriiietins, and scintillans are far more difficult 
to arouse." May not the same be true in nature generally, and 
may not the same strain arise again and again, commonly fail- 
ing to persist because as a rule all conditions are against it } 

6. Mutability is distinct from fluctuating variability. Darwin 
regarded the new type as built up by the operation of selection 
upon fluctuating variability, establishing a new type by the 
gradual accumulation of favorable variation, all others (inter- 
mediates) being exterminated. De Vries regards mutability as 
distinct from fluctuating variability, and considers that he has 
presented experimental evidence to show that it is entirely com- 
petent to give rise to new forms suddenly, without intermediates 
and without the aid of selection. He of course believes that all 
types, both old and new, are subject to fluctuating variability, 
and that through selection some improvement is possible, but that 
this is not the sole or principal method of securing new types. 

7. " The mutations take place in nearly all directions." Some 
are larger, some are smaller than the parent ; some stronger, 
others weaker; some plainer, others more brilliant. The species 
is not, therefore, drifting ; it is sending out new types from all 
sides. 

SECTION IV — AMERICAN EXPERIENCES 

The experiments of De Vries are strongly confirmed by the 
experience of breeders, especially in the production of new varie- 
ties of fruits and vegetables. Many of these have been so long 



I30 



VARIATION 



under cultivation that nothing is known of their origin. Of others, 
on the contrary, the hfe history is well known. 

When Europeans peopled America they naturally brought 
with them their fruits, their vegetables, their grains, their grasses, 
and their domestic animals. The new country was rich in native 
species, both plant and animal, but the European species had 
the advantage of being better known and better adapted to the 
special needs of man. Accordingly, wherever the introduced 
varieties succeeded, the corresponding native types were neg- 
lected ; but when the European varieties failed, then the natives 
were developed. It is from this latter class that some important 
observations may be made.^ 

The gooseberry .2 The large English gooseberry was too tender 
for the American climate, and withal was exceedingly liable to 
mildew. Native varieties flourished widely in the forests. Unfor- 
tunately the varieties bearing the largest berries were exceedingly 
thorny, both on bush and fruit. Side by side, however, with these 
prickly sorts were smooth varieties, free from "prickers" both on 
fruit and bush. These were freely transplanted to the gardens 
of the pioneers and furnished an acceptable fruit. ^ In good time 
they developed improved sorts, — first the Houghton, a seed- 
ling originated by Abel Houghton of Lynn, Massachusetts, some- 
time in the early forties. Then came the Downing, a seedling of 
the Houghton, first described in 1853, the fruit of which is said 
to be " the largest yet known, being about twice the size of the 
Houghton's seedling, its parent ; it is pale or light green, without 
any blush, and smooth. The skin is very thin and the fruit as 
delicate and tender as any European gooseberry on its native 
soil. The flavor and aroma are perfect." 

Bailey observes in this connection, " This berry, now known 
as the Downing, is the standard of excellence in American 
gooseberries, and is probably grown more extensively than all 
other varieties combined ; and yet it is only two removes from 
the wild species." 

1 L. H. Bailey, Evolution of our Native Fruits [The Macmillan Company, 
New York]. 

2 Ibid. pp. 389-399- 

^ The writer remembers very well as a boy searching the woods, and espe- 
cially the swamps, of Michigan for these smooth varieties for transplanting. 



MUTATIONS 



131 



Is not this a natural mutation in the truest sense of the term ? 
If not, then it is merely a question of terminology and definition. 
The fact remains that it arose suddenly, a distinct type, and 
remains true with no characteristics of a hybrid. We need a term 
for this sort of thing which is occasionally occurring everywhere 
in nature, in our gardens and in our herds, and I know of none 
better then the one already in use — mutation. 

The strawberry.^ The wild strawberry grew everywhere in 
northern North America. There were not only many distinct 
types of the red, but, like the native raspberry and the blackberry, 
it had everywhere its albino race. Good progress had been made 
in the cultivation of the native strawberries, and without doubt 
good varieties would in time have developed ; but the introduction 
of the Chilean berry (the parent of most present varieties) seems 
to have put a stop to this. The most promising of all native 
strains was the Fragaria Chilocnsis, a native to Oregon and the 
Pacific coast ; but, as Bailey observes, " the garden progeny of 
its South American branch is already so good that there is little 
reason for returning to the wild for a new start." Here is a curi- 
ous instance of the successive supplanting of varieties. European 
sorts were vanquished by developments of New England natives. 
Then the wild type of Oregon came into the struggle and 
threatened to supplant them both, for it was full of promise. 
But its prosperity was its own defeat, for its own Chilean 
brother has now supplanted everything in that it is the stock 
which is furnishing our improved varieties. Any student of this 
subject will recognize the comparative readiness with which these 
new types spring up. 

The blackberry.- The blackberry grows wild l^oth in America 
and in Europe, but is .said to be cultivated only in North America. 
It is not more than fifty years since improved varieties were 
introduced, and its real cultivation dates only from about 1875. 

There are two principal types of the wild blackberry growing 
in the northern United States: (i) the "high bush," long and 
luscious, loving the shade, represented in its cultivated types, 
according to Bailey, by the Taylor and the Ancient Briton ; 

1 L. H. Bailey, Evolution of our Native Fruits, pp. 424-432. 

2 Ibid. pp. 29S-330. 



132 VARIATION 

(2) a smaller variety growing in sunny, open places and bearing 
small, round, loose-grained fruits, ripening late and exceedingly 
sour. This type is represented in cultivation by Lawton, 
Kittatinny, Snyder, Agawam, Erie, and others. Neither of these 
yielded readily to cultivation and restraint, and this fact served 
in an early day to earn an evil reputation for what Professor 
Card calls this " gypsy of the fruits." Nevertheless, they yielded 
to persistent efforts, and have given rise, as Bailey puts it, " to a 
host of varieties . . . very many of them wildings, or chance 
bushes found in fence rows." 

The first-named variety was the Dorchester, introduced about 
1 84 1. Its exact origin is unknown, though its originator (prob- 
ably Captain Lovett) is known to have transplanted wild plants 
for many successive years. Whether this first civilized gypsy 
was a sport or simply a strain improved by selection is not now 
capable of proof, and yet its constancy is good presumptive 
evidence. 

Wilson's Early was known in 1854, the Holcomb in 1855, and 
in 1857 the Lawton (first called New Rochelle) was introduced, 
being at once declared superior to the Dorchester. Of these the 
Wilson was "discovered in the wild about 1854 by John Wilson 
of Burlington, New Jersey"; and the Lawton, formerly New 
Rochelle, " was found in the town of New Rochelle, New York, 
by Lewis A. Secor." These two strains hav^e given rise to 
numerous distinct modern varieties. The "loose-cluster" strains 
are regarded by horticulturists as the descendants of the Wilson. 
The origin of certain other varieties seems to be as follows : 

In 1870 Mr. William Parry, of New Jersey, "selected a 
healthy young Dorchester and planted it in the same hill with a 
strong, healthy Wilson's Early (for breeders), located far away 
from any other blackberries." ^ In 1875 the seed from some of 
the largest berries growing on the Wilson were planted. One 
plant only was regarded as valuable, and all others were destroyed. 
This new strain was named Wilson Junior. The fruit was " large, 
early, and very fine," and so prolific that in 1884 "one acre 
yielded i loi- bushels of fruit, by the side of five acres of Wilson's 
Early in the same field, with the same culture, which averaged 

1 Bailey, Evolution of our Cultivated Fruits, p. 316. 



MUTATIONS 133 

but 53 bushels." The Eureka was produced in exactly the same 
way in 1877. In 1879 Rioter and Farmer's Glory were also 
produced from berries growing on the Wilson, and Gold Dust 
and Primordian from berries growing on the Dorchester. The 
Gold Dust was remarkable for the fact that its entire crop ripened 
within a period of four days. It was th-us distinct from all other 
blackberries in at least one important character. 

The Sterling Thornless arose as a chance seedling of the 
Wilson on the farm of John Sterling at Benton Harbor, Michigan. 
It is, as its name indicates, destitute of thorns, and is a distinct 
mutation, to be carefully distinguished from other strains of 
thornless blackberries, which, according to Bailey, are " specific- 
ally distinct from the common bush blackberry." 

Plums.i According to Bailey not a single commercial variety 
of plum has ever originated from the native stock of New Eng- 
land, New York, Pennsylvania, or Michigan. This is partly 
because the European sorts thrive well and partly because the 
natives of this region " are less prolific of large-fruited forms than 
those farther west." 

Some excellent varieties have arisen, however, from native 
stock elsewhere. The Miner was produced from seed of native 
stock planted in 18 14 by William Dodd in Knox County, 
Tennessee. The Robinson was a seedling from North Carolina 
stock. Wayland " came up in a plum thicket in the garden 
of Professor H. B. Wayland of Cadiz, Kentucky," and was 
introduced about 1876. The Missouri apricot was found wild 
in Missouri. The Golden Beauty was found in the same way 
in Texas, the Pottawattamie in Tennessee, and the Newman in 
Kentucky. 

The Wolf originated from seed gathered from wild trees in 
Iowa. The Pottingstone was found on the bank of Potting- 
stone Creek, Minnesota, and the Quaker was found wild in Iowa. 
Literally scores of well-defined varieties have arisen from native 
stock. It would be too much to say that none of these are hybrids. 
Undoubtedly many of them are the product of crossing, but this 
origin cannot be consistently claimed from chance seedlings 
found in a thicket of ordinary wild stock. Mutation, whatever 

1 Bailey, Evolution of our Native Fruits, pp. 170-226. 



134 



VARIATION 



it is, must be credited with having produced many new forms 
spontaneously. 

Grapes.^ " North America is a natural vineyard," says Bailey, 
and yet with the most skillful and persistent attempts to culti- 
vate the European varieties for wine making, they have not suc- 
ceeded. Under these circumstances nothing is more natural 
than that valuable native varieties should arise, providing the 
capacity was inherent in the species. 

John Adlum wrote, about 1823, "The way is to drop most 
kinds of foreign vines at once and seek for the best kinds of our 
largest native grapes." He is to be remembered for the intro- 
duction of the famous Catawba, which was " found wild in the 
woods of Buncombe County in extreme western North Carolina 
in 1802." 

The Catawba is, therefore, almost certainly a sport of the 
wild grape growing in profusion in that region. In 1843 came 
the Diana, a seedling of the Catawba. 

In 1840 Mr. E. W. Bull bought a house in Concord. Some 
seedlings of wild grapes sprang up about it, one of which fruited 
in 1843. It was so excellent in quality that all others were 
destroyed and the new variety was named the Concord. This 
seedling has since given us the Worden, Moore Early, Pockling- 
ton, Eaton, and Rockland, of which the first has long been 
famous. The Concord, itself a mutant, seems to have been 
peculiarly rich in possibilities for still other races. 

" In the year 182 1 Honorable Hugh White, then in the junior 
class in Hamilton College, New York, planted a seedling vine 
in the grounds of Professor Noyes, on College Hill, which still 
remains, and is the original Clinton." 

These are only a few of the many varieties of grape of Ameri- 
can origin, tracing directly to wild native stock. 

Lost possibilities. Had other domesticated plants and animals 
brought from Europe succeeded less admirably, what enrichment 
might have come through the native flora and fauna of America ! 

The prairie chicken would have been improved if the domestic 
hen had not succeeded. The turkey was a new thing and was 
therefore seized upon. The buffalo would not now be extinct 

1 Bailey, Evolution of our Native Fruits, pp. 1-126. 



MUTATIONS 135 

if cattle had acclimated less successfully. Native grains other 
than maize would have been developed had it not been for this 
competition, and native grasses have not lived up to their possi- 
bilities. This is through no fault of theirs, though we still lack 
" the best American grass." 

SECTION V — ECONOMIC SIGNIFICANCE OF MUTATIONS 

Because of the waywardness of sports, — the impossibility 
of predicting their appearance, the readiness with which they 
disappear when interbred with the parent stock, and their very 
frequent inability to reproduce at all, — because of all these con- 
siderations it has become fashionable to declare sports in general 
to be of slight economic importance and unworthy the breeder's 
serious attention. The only course left open for improvement is, 
therefore, the slow one of gradual accumulation through selec- 
tion of minute but favorable variations, according to the theory 
of Darwin. 

The best of evidence exists, however, for believing that this 
is a hasty and unwarranted conclusion, and that many, if not 
indeed most, of our really valuable new types have arisen sud- 
denly as mutations and not gradually through infinitesimal differ- 
ences, as is commonly supposed. The experiments of De Vries 
and the American varieties of fruits both come near enough to 
the origin of types to more than warrant this view of the situa- 
tion and to afford ground for the greatest hope that unsuspected 
possibilities still exist in many if not most domesticated species, 
— possibilities of spontaneously giving off varieties representing 
essentially new combinations of the characters of the species and 
consequently possessed of different and perhaps enhanced eco- 
nomic value. The work of Luther Burbank^ and of our commer- 
cial seedsmen add confirmation to this hope, which, if well 
founded, promises new methods in breeding and vastly increased 
possibilities for improvement. 

The small numbers involved in animal breeding reduce enor- 
mously the chances of mutations appearing ; and yet nearly every 

1 W. S. Harwood, in The Century Magazine, March and April, 1905 ; also New 
Creations in Plant Life [The Macmillan Company, 1906]. 



136 



VARIATION 



species has thrown off its albino variety, which in most cases is 
easily propagated. Hornless cattle occasionally appear in nearly 
all breeds, and the type is comparatively easy of preservation. 
It is more than likely that the different types in the larger 
breeds, which breeders find so difficult to break up, are in 
reality quite distinct. 

In future chapters dealing with the measurements of variation 
and the statistics of heredity in general, it will appear that even 
fixed types afford sufficient deviation to keep a breeder busy 
with selection ; in other words, that the animal breeder dealing, 
as he is, with small numbers will always find sufficient variation 
to lead him to suppose that he is getting results of his selection 
even when he has not shifted the center of variation the slight- 
est. Much that passes for breeding is nothing more than this 
ineffectual multiplication, and it is not too much to say that 
hundreds of breeders and thousands of animals have lived and 
died without affecting the breed in the slightest. 

The writer is strongly of the opinion that while selection is a 
powerful agent for "shaping up" and "finishing off" a fairly 
acceptable type, and while it is the only means of deciding 
what shall live and what shall disappear, yet much of the real 
advance in both animal and plant breeding is likely to come 
through distinct offsets which are now called mutations, and 
which in Darwin's time and until recently were erroneously, if 
not reproachfully, denominated " sports." 



SECTION VI — BIOLOGICAL SIGNIFICANCE OF 
MUTATIONS 

Too much mystery has surrounded this matter of sports, 
and there has been a too ready tendency to evoke the aid of 
latent characters to explain this and almost every other unusual 
phase of evolution. 

In truth, there is no more mystery about mutations than 
about heredity in general, which is a complication of mysteries. 
It is not a question of latency but of relative prominence of 
characters, of the possible loss of a racial peculiarity, or, what 



MUTATIONS 137 

is more likely, a new combination of the elements out of which 
characters are made up. 

Every new being is the result of a new combination of racial 
faculties transmitted from two family lines, possibly differing 
in essential particulars. This new combination is certain to 
throw some characters into prominence and others into the 
background, and results occasionally in strikingly new effects. 
This is usually the case in hybridization, but it follows in less 
degree in ordinary reproduction, which differs from hybridiza- 
tion more in degree than in kind. 

Again, many characters, though exceedingly noticeable, rest 
after all upon a comparatively simple basis. Such, for example, 
is pubescence in plants, which depends upon the activity or 
non-activity of a few cells in developing a hairy growth. Nearly 
all species present both forms, — the one in which the character 
is present, and its opposite in which it fails to develop. Simi- 
larly, almost any character may fail, giving rise to a distinctly 
new creation. If the failure is not at a vital point it may be 
transmitted, in which case a new type has arisen. 

The origin of a new type by the addition of a character is, 
biologically considered, much more complicated and dif^cult of 
understanding; yet even this is not beyond some degree of 
comprehension. The probability is that what we call racial 
characters are less complicated than we may at first suppose. 
The unlearned savage could scarcely believe that the almost 
infinite variety of colors of natural objects are due to different 
combinations of very few primaries. The effects produced by 
three-color printing are almost beyond belief, yet we are fully 
advised as to the real basis for all these variations ; while the 
effects are striking, the means are simple. 

So it is, we may imagine, in the ultimate make-up of what we 
call racial characters : their elements are doubtless fewer than 
we have supposed, and the possibilities of their combinations 
and recombinations are greater than we have hitherto imagined. 
Whether all possible combinations of these elements actually 
take place we do not know, but all facts go to show that they 
occur in great variety, the most striking and permanent of which 
we call mutants. 



138 VARIATION 

If a new race is produced by hybridization, then a new com- 
bination of characters has been effected, and it is fair to assume 
that the combination is richer in possibihties and possesses a 
larger number of characters than did either parent. Mutation 
teaches that new assortments of characters may take place, in 
some cases at least, without hybridizing. 

If a racial character, as color or hairiness, is lost, we recognize 
the new type and name it as a new creation. It may be more 
valuable to us than its parent, but it must be recognized biolog- 
ically as having lost something to which it was racially entitled. 

Again, if all normal characters acquire an unusual develop- 
ment, relatively or absolutely, as in giants, or if their develop- 
ment is abnormally arrested, as in dwarfs, we again recognize 
the new departure, and it is a good mutation. 

Still again, if certain characters only undergo change in devel- 
opment, while others remain normal, then relative values are 
changed, the effect is altered, and we recognize a different type. 
This, too, is a good mutation, provided the new relation persists. 
All these changes can be worked with the normal characters 
of the race, without the introduction of new characters or even 
the supposititious aid of latent characters. Soberly considered, 
these changes are none other than the student of biology would 
expect, unless indeed racial characters are bound together rnuch 
more rigidly than present evidence would lead us to suspect. 

Summary. Not all variations are continuous and connected 
with the type by insensible differences. Some deviations are dis- 
continuous, with a tendency for future variations not reverting to 
the main type but clustering about a new center of variability, thus 
setting up a new type. Such a deviation is called a mutant, and 
new strains may arise in this manner, as well as by the slower 
Darwinian method of heterogeneous variation, out of which new 
types are established by the slow process of selection. 

Both the experience of breeders — especially with new varie- 
ties in America — and numerous instances of experimental evi- 
dence show conclusively that new strains not only may, but in 
actual practice do, originate in this manner, suddenly and com- 
pletely, without any apparent preparation and with little tendency 
to revert to the original or main type, which continues as before 



MUTATIONS 1 39 

Mutants, like their parent types, are subject to fluctuating 
variability, which is a necessary law of reproduction, and they 
may be improved — that is, shaped up — by judicious selec- 
tion, but their principal characters and main trend were fixed 
when the type arose. 

ADDITIONAL REFERENCES 

Alijixism. (A critical study of its causes.) By E. Pantanelli. Experiment 
Station Record, XV, 55. 

Atavic Mutation of the Tomato. By C. A. White. Science, XVII, 
76-78, 234-235. 

Atavism in the Potato. By S. Rhodin. Experiment Station Record, 
XI, 710. 

Determinate Mutations. (De Vries and others quoted.) By M. M. 
Metcalf. Science, XXI, 355-356. 

Evolution and Adaptation. By T. H. Morgan. Science, XIX, 
221-225. 

Evolution without Mutation. By C. B. Davenport. Science, XIX, 215. 

Inheritance of Monstrosities. (Experiments of -twelve years.) By 
Hugo De Vries. Experiment Station Record, XI, 546. 

Mutation and Selection. (What causes mutations.? Are they all in 
one direction?) By M. M. Metcalf. Science, XIX, 75-76. 

Mutation in the Tomato. By C. A. White. Science, XIV, 841-S44. 

Mutation Theory. (A review of Species and Varieties.) By C. B. Daven- 
port. Science, XXII, 369-372. 

Mutation Theory of De Vries. (Twenty-eight lectures by the author 
at the University of California, 1904.) Experiment Station Record, 
XVI, 745- 

Mutation Theory of De Vries. By D. T. McDougal. Experiment 
Station Record, XIII, 324-619; XIV, 226, 526. 

Mutation Theory of Organic Evolution. (A brief but pointed sur- 
vey of the subject.) By W. E. Castle of Harvard University. Science, 
XXI, 521-543; from standpoint of animal breeding, 521-524; from 
standpoint of cytology, 525-528. 

Mutations in Plants. By D. T. McDougal. American Naturalist, 
XXXVII, 737-770; also in Experiment Station Record, XVI, 23. 

Origin of Species. By Hugo De Vries. Science, XV, 721-729. 

Origin of Species through Selection contrasted with their 
Origin through Appearance of Definite Varieties. By T. H. 
Morgan. Popular Science Monthly, LXVII, 54-66. 

Prepotency of Individuals with Abnormal Variation or Muta- 
tion. (A study of cats with extra toes.) By H. B. Torrev. Science, 
XVI, 554-555- 



I40 VARIATION. 

Some Causes of Saltatory Variation. By C. H. Eigenmann. Pro- 
ceedings of the American Association for the Advancement of Science, 
1900, XLIX, 207. 

Sports. (Author concludes there are other laws than Mendel's and Galton's.) 
By C. B. Davenport. Science, XIX, 151 ; also in Experiment Station 
Record, XV, 753. 

Sports on Grapevines. By J. C, Talback. Experiment Station Record 

XV, 478. 

Sports; the Peach-Nectarine. Journal of the Royal Horticultural So- 
ciety, XXVI, 596-598; also in Experiment Station Record, XIV, 45. 

The Mutation of Lycopersicum. By C. A. White. Popular Science 
Monthly, LXVII, 1 51-162. 

The Mutation Theory'. (A defense.) By Thomas L. Casey. Science, 
XXII, 307-309. 

The Orkjin of a White Blackberry. By Luther Burbank. Exper- 
iment Station Record, XIV, 1071. 

Theory of Mutations. By A. A. W. Hubrecht. Popular Science 
Monthly, LXV, 205-223. 



Part II — Causes of Variation 



INTRODUCTION 

Variation is at once the most promising agent for improve- 
ment and the most powerful and subtle force for undermining 
and destroying what has already been attained. Because of this 
and with a view to their possible control, the breeder is especially 
interested in the causes that lead to deviation in plant or animal 
characters. 

It is said that it is yet too early to inquire into the causes of 
variation, because our stock of accurate knowledge is too limited 
to permit a settlement of this most complicated cjuestion. That 
the matter cannot be fully settled in the present state of knowl- 
edge is beyond question, but the writer does not share the opin- 
ion that discussion at this stage of proceedings is unprofitable. 

The student of general evolution may well assume the role of 
a curious but disinterested observer, note what passes before 
his eyes, and take his choice as to the questions that shall 
engage his attention. Not so with the farmer and breeder. His 
funds are tied up in his animals and his plants. He is breeding 
them not for amusement but for profit, and he is interested in 
results not thousands of years hence but in those that may be 
confidently expected within the limits of a lifetime. 

He above all men, therefore, is interested in variation and 
the causes that induce it ; and we are bound in his interest to 
study the question assiduously, to determine what is known 
and what is not known on this most important point, and to 
indicate as well as we are able the direction from which further 
light may be expected. To this end everything is important 
that is connected with variability in a causative way, whether 
its effect is upon either the form or the function of living 
matter. 

141 



CHAPTER VII 

THE MECHANISM OF DEVELOPMENT AND DIFFERENTIATION 

Before specific inquiries can be profitably made into the causes 
of variation it is necessary to become fairly familiar with what 
is known of the essential constitution of living matter and of its 
manner of growth and differentiation. 

After attention has been bestowed for a time upon these con- 
siderations, it will be evident to the student that here, in the 
inner workings of living matter, are fundamental causes of pro- 
found variations, even in protoplasm seemingly the most stable. 

SECTION I — PROTOPLASM THE PHYSICAL BASIS 
OF LIFE 

Protoplasm is a general name for all matter that is endowed 
with life, but the student must never forget that the biologist, 
like the chemist, is dealing with matter composed of well-known 
chemical elements united in definite proportions. The known 
differences between living and non-living matter are, for our 
purposes, the following : 

1. Living matter is endowed with a mysterious force called 
life. 

2. Matter so endowed has a much more complicated chemical 
composition than has non-living matter, or than can be main- 
tained after the life principle has departed. Living matter at 
death, therefore, breaks up (or down) into ordinary chemical 
compounds. The true constitution of living matter cannot, 
therefore, be determined by any known methods of analysis, 
which reveal only the elements involved but not their exact 
relations during life. 

3. Matter endowed with life is able to appropriate to itself 
other outlying matter and to increase its bulk through growth. 

142 



THE MECHANISM OF DEVELOPMENT 143 

4. This growth is not of bulk merely, but it is attended by 
differentiation, so that one part is distinctly different from 
another. 

5. As growth proceeds bits of this bulk are thrown off, each 
of which constitutes a new individual capable of independent 
existence, — reproduction. 

6. The new individual is substantially, but never exactly, 
like the one from which it arose, and here lie the chief mys- 
teries of breeding. In reproduction there are no duplicates. 

Nothing approaches this in the inorganic world save crystal- 
lization. Crystals add matter to their bulk and thus may be 
said to grow. Moreover, the matter is added in an orderly 
manner, resulting in a kind of definite structure with exact 
angles always the same, but nothing like differentiation exists. 
One part of the crystal is like another ; it has no power of 
reproduction and is possessed of no force comparable with life. 

The student should early learn that the field of biology is 
distinct, but he should also fully realize that it lies within and 
not outside the range of chemistry, and that living matter is not 
freed from its ordinary affinities by reason of its association with 
life, but on the contrary it continues as before to be subject to 
the ordinary physical and chemical relations of matter generally. 
If he can do this, he will simplify many of his difficulties. 

SECTION II— THE CELL THE UNIT OF STRUCTURE 

If a bit of liver, bone, wood, or any other form of plant or 
animal tissue be examined under the microscope, it will be found 
to possess a definite structure, and to consist of a large number 
of separate divisions, each filled with a gelatinous mass called 
protoplasm. These separate divisions or cells are apparently 
alike throughout the substance of any particular tissue, - — as 
the liver, — but they differ greatly in different tissues of the 
same body (bone, muscle, brain). Biologists have been unwilling 
to consider the individual as the unit, because he is too large 
and his structure and activities are too complicated. They have, 
therefore, chosen to regard the individual as a colony of many 
and variously differentiated cells. 



'44 



CAUSES OF VAklA'LION 



In assumiiif^ the rc-ll as a unit many structural (liffu ulties 
were s(jlvc(l to the entire satisfaction of the anatomist, but the 
l>hysi(jlo};ical and evolutionary problems were ( on)|)li( ated rather 
than simplified, brcansc this entire colony of many different cells 
and activities — heart, liai^t^s, liver, muscles, nerves, etc., ivith 
their many and diverse functions — sprani^ originally from a 
single cell ; moreover, this colony will throw off a succession (jf 
single c;ells, each of which will undergo s]jec:ific and orderly 
development and '(\x\\\Wj produce a colony like the pare^it. This 
bein^ true, the cell cannot be regarded as the ultimate unit oi 
living matter, unless we assume sf>mc kind of unity between all 
the cells ; some kind of intercellular force to insure that differ- 
entiation shall take place at the jiroper points and stages, — 
otherwise the original cell wfjuld develop into a lump of proto- 
plasm or into a ( olony of cells all alilce. 

The single cell frrtm wh'ch a new individual is to develop 
(the "germ cell" or mother cell) is gifted with ])otentialities 
for Ihe entire being, with all its ( om])lications of structure and 
with all its variety of function, liiologists at one time were 
inclined to rc;gard this germ < ell as " totipotent," that is, able 
to develop into almost any kind of stru( ture depending upon 
the surroundings. This view could not hold because different 
germ cells under identical conditions of life develop each into 
its own species. 

The cause of differentiation, therefore, lies ])rimarily within, 
and the germ cell is to be regarded as gifted with unlimited 
powers of (l(:velo|)n)ent only within the characters that belong to 
the species. 

Specific protoplasm is, therefore, possessed of s|)ecific prf)per- 
ties as truly as is any cluMiiical substance, and all the characters 
of structine or function belonging to the mature individual 
are to be regarded as in some way " inlierent in the germ." 
The cell is, therefore, like the individual, too laige and too 
complicated to be considered as the ultimate unit of living 
matter. 

This view is upiield not only upon theoretical grounds but 
also by the known facts of its com|)licated struct luc ;uid its re- 
markable behavior during cell division and growth, a subject 



'i'lllv Ml'lCHANISM ()!'• l)KVI<:iX)l'MKNT 145 

which it were well to consider before proceechn^^ furllier with 
the search after the " iiiliniate unit of nvin<^ matter," and 
therefore of f^nnvth, oi differentiati(jn, and of variability. 



SECTION 111— THK MKCIIANISM OF CKLL DIVISKJN 
(MITOSIS) 

Growth in the sense of increase of size is the direct result of 
cell division. Lar^e bodies do not have larger cells than small 
ones, but they have more of them. Growth is, therefore, in 
proportion to cell division, — the mechanism of which is exceed- 
ingly suggestive of the methods by which lines of descent are 
preserved and the proi)er development assured. 

When the pnjtoiilasm of an ordinary growing cell, |)lant or 
animal, has absorbed material until it has reached a certain maxi- 
mum size, it then prepares for division. This is not a lump 
division in which the new cells each get one half of the bulk of 
the jjarent cell, but it is (jualitative as well as cjuantitative, and 
is based on an exceedingly orderly procedure, which insures not 
only that each daughter cell shall receive its share of the mass 
but also that this share shall be identical in quality with that 
inherited by the sister cell of the same divisicjn. 

Those portions of the cell contents most intimately concerned 
in the process of divisicm, and therefore of chief interest here, 
may be briefly described as follows : 

Floating in the general protoplasmic mass (the cytoplasm) is 
a small body (the nucleus) of greater density than its surround- 
ing matter and the evident seat and initial jjoint of all construc- 
tive processes. 

Scattered through the mai^s of the nucleus and generally, but 
not always, in the form of minute granules is the so-called 
"chromatin matter," named from its intense reaction to staining 
agents. 

These granules of which the chromatin matter is (apparently)' 
composed arc the "chromatin granules" of some authors, the 

^ The word "apparently" is inserted because the granular character of chro- 
matin matter has not in every case been made out, and because its granular 
character is less pronounced at some times than at others. 



146 CAUSES OF VARIATION 

" chromomeres " of others, the "microsomes" of still others, 
and the " ids " of Weismami. 

Lying generally in the cytoplasm just outside the nucleus will 
commonly, but not always, be found an extremely minute highly 
staining body, the centrosome, about which, when division is 
about to occur, the near-by matter is thrown into radiating lines 
like iron filings about the poles of a magnet, giving the whole a 
kind of starlike appearance. 

These are the portions of the cell most concerned in cell 
divisions, and their special characters are most pronounced and 
the differences most distinct just previous to the act of division, 
and least well marked in the cell during its "resting stage" 
between divisions. 

The actual process of cell division whereby one cell gives 
rise to two and by which growth is attained is essentially as 
follows : 

When division is about to take place the chromatin matter 
(granules) assumes the appearance of a fine network running 
through the mass of the nucleus, the granules looking like beads 
strung upon a thread. This network commonly, though not 
always, condenses into a ribbon or thread (the spireme), which, 
however, speedily breaks up transversely into a definite num- 
ber of segments, generally in the form of short rods, straight or 
curved (the chromosomes). Whether or not the reticular or net- 
work form passes through the spireme stage, the result is always 
the same ; namely, the chromatin matter becomes divided into 
a definite number of chromosomes. Here are two remarkable 
and significant facts ; first, the miniber of cJironiosomes is con- 
stant in all individuals of the same species ; and second, " /;/ all 
species arising by sexual reproduction the number is even.'' ^ 

While the chromatin matter has been engaged in breaking up 
(or down) to form the chromosomes, another significant process 

1 Wilson, The Cell, p. 67. The author here gives the number of chromosomes 
characteristic of certain species as follows: some of the sharks, 36; mouse, 
salamander, trout, and lily, 24; ox, guinea pig, and onion, 16; grasshopper, 12; 
Ascaris, 4 or 2 ; the crustacean Arleinia, 168; man, 16 or possibly 32. In this 
connection it is worthy of note that varieties of the same species often differ in 
the number of their chromosomes, the significance of which variation has not 
yet been determined. 



THE MECHANISM OF DEVELOPMENT 147 

has been going on. The centrosome has divided and the two 
new bodies derived from it have separated and migrated to 
opposite sides of the nucleus, each surrounded by its radiating 
Unes, in which condition they are known as "asters" (stars). 

During this migration the asters are generally (not always) 
visibly connected by lines, but in either case by the time they 
have reached opposite sides of the nucleus they will be seen to 
lie at opposite ends of a spindle-shaped body (the amphiaster) 
consisting of lines, among which lie the chromosomes. 

Matters are now ready for the final and significant acts of 
cell division. The chromosomes arrange themselves end to end 
along the equator of the spindle, and at right angles to its axis ; 
whereupon each chromosome splits lengthwise, one group of 
halves migrating to one aster (centrosome), the other to the 
other, where each clusters about its own center, forming a new 
nucleus with its centrosome. The cell wall now becomes con- 
stricted, dividing the cytoplasm approximately equally (some- 
times very unequally) between the two new cells, and the division 
is complete. The resting stage ensues, during which preparation 
is made for another division ; indeed, the centrosome occasionally 
divides, in anticipation of the next division, even before all the 
details of the first division are complete. For a graphic outline 
of the complete process of mitosis see Figs. 20 and 21. 

This, in general, is the process of cell division which, with 
more or less variation, attends all growth. The significant facts 
brought to light in this complicated process are: (i) that the 
number of chromosomes is constant for all individuals within 
the species ; (2) that for all forms arising by sexual reproduc- 
tion the number is even ; (3) that however its details may vary, 
cell division consists essentially in a splitting of the chromo- 
somes, by which each daughter cell secures (apparently) an 
exact equivalent of what is received by the other daughter cell 
of the same division. Cell division is therefore not a lump 
division of the cell mass, but it is meristic, insuring a strictly 
qualitative division in which one half of each chromosome 
descends to either daughter cell.^ 

1 These same facts have added significance when considered in connection 
with the germ cells, reproduction, and the problems of heredity. 



VARIATION 




/ ''\ 






Fig. 20. Diagrams showing the prophases 
of mitosis 

A, resting cell with reticular nucleus and true nucleolus : at c the attraction sphere containing 
two centromoses. B, early prophase : the chromatin forming a continuous spireme, 
nucleolus still present; above, the amphiaster («). C, D, two different types of later 
prophases : C, disappearance of the primary spindle, divergence of the centrosomes to 
opposite poles of the nucleus (examples, some plant cells, cleavage stages of many eggs) ; 
D, persistence of the primary spindle (to form in some cases the "central spindle"), 
fading of the nuclear membrane, ingrowth of the astral rays, segmentation of the spireme 
thread to form the chromosomes (examples, epidermal cells of salamander, formation of 
the polar bodies). E, later prophase of type C: fading of the nuclear membrane at the 
poles, formation of a new spindle inside the nucleus ; precocious splitting of the chromo- 
somes (the latter not characteristic of this type alone). F, the mitotic figure established ; 
ep, the equatorial plate of chromosomes. — After Wilson 



THE MECHANISM OF DEVELOPMENT 



149 



SECTION IV— CELL DIVISION WITH AND WITHOUT 
DIFFERENTIATION 

The accomplishment of this minutely accurate division of cer- 
tain portions of the mother cell between the daughter cells at 
division suggests two points : (i) that the matter thus carefully 







/ J 

Fig. 21. Diagrams of the later phases of mitosis 

G, metaphase: splitting, of tlie chromosomes {cp)\ n, the cast-off nucleolus. H, anaphase: 
the daughter chromosomes diverging, and between them the interzonal fibers {if), or 
central spindle; centrosomes already doubled in anticipation of the ensuing division. 
/, late anaphase or telophase, showing division of the cell body, midbody at the equator 
of the spindle, and beginning of reconstruction of the daughter nuclei. /, division com- 
pleted. — After Wilson 

divided is of special importance in shaping the activities of future 
cells ; (2) that daughter cells so provided should be identical, 
and their after growth should not only be alike but should 



150 



CAUSES OF VARIATION 



also be similar to that of the mother cell from which they are 
descended. 

For all cell division within the same tissue this latter is true ; 
that is to say, in the growth of liver tissue, bone tissue, or any 
other specific structure the cells appear to be identical and 
their resulting growths alike. But it must not be forgotten that 
these different tissues all arose originally from a single cell ; in 
other words, that some cell divisions are attended by differenti- 
ation. When .'' How } Here lies the chief mystery of variation. 
The mechanism of cell division would seem to be specially 
designed to prevent deviation and to insure absolute transmission 





^ B 

Fig. 22. Pathological mitosis in epidermal cells of salamander caused by poisons 

A, asymmetrical mitosis after treatment with 0.05% antipyrin solution ; B, tripolar mitosis 
after treatment with o.-~/'/q potassic iodid solution. — After Wilson, from Galeotti 

from mother cell to daughter cell. It does not account for or 
indeed appear to admit of differentiation of tissues or variation 
in growth. But differentiation does take place and variation is 
a fact to be in some way explained. 

Irregularities in cell division. Not all cell division, it is true, 
proceeds with the regularity and perfection of plan indicated in 
the description, which is the common method in higher animals 
and plants and may therefore be regarded as fairly typical. The 
known abnormal cases are of several distinct kinds : 

I. Asymmetrical mitosis, in which the chromosomes are not 
equally distributed to the daughter cells, most of them massing 



THE MECHANISM OF DEVELOPMENT 



151 



at one pole, some of them perhaps being lost altogether in the 
mass of the cytoplasm. 

2. Multipolar mitosis, in which the number of centrosomes is 
more than two and the resulting daughter cells three or more. 

Both these abnormal processes, however, are characteristic of 
abnormal growths, such as cancers and tumors, and are therefore 
considered as pathological. It is a suggestive fact that such 
irregularities may be artificially produced by poisons and other 




Fis 



D E F 

Pathological mitoses in human cancer cells 



A, asymmetrical mitosis with unequal centrosomes ; B, later stage, showing unequal distri- 
bution of the chromosomes ; C, quadripolar mitosis ; D, tripolar mitosis ; £, later stage ; 
F, trinucleate cell resulting. — After Wilson, from Galeotti 

chemical substances such as chloral, quinin, nicotin, antipyrin, 
cocain, etc.^ (See Figs. 22 and 23.) 

3. Amitotic division,'^ — that is, division without the forma- 
tion of the amphiaster or the splitting of the chromosomes. 
This form of cell division is effected by constriction, resulting 
simply in a lump division of the mass of the nucleus, without 
reference to qualitative considerations. In this case the daughter 
cells would not, presumably, be alike. This form of cell division 

1 Wilson, The Cell, pp. 97, 98. Ibid. p. 114- 



152 



CAUSES OF VARIATION 



is of rare occurrence, is never known in embryonic tissues, and 
is characteristic of tissues "on the way towards degeneration." ^ 

4. Quite generally imicellular organisms display extreme 
irregularities in mitosis, some species omitting one and others 
another of the processes typical in higher species. Prominent 
among these deviations is the failure of chromatin granules to 
unite to form definite chromosomes. In place of this the indi- 
vidual granules themselves divide, suggesting that fission of 
the grannies is the elcnioitary and essential feature of nuclear 
division? 

Other minor deviations are known, though much of the 
field is yet unworkcd. These may account to some extent for 
differentiation during cell multiplication, and yet so far as is at 
present known all processes that do not accomplish an ecjuitable 
division of the chromatin granules through the splitting process 
are looked upon as distinctly pathological. Normal cell division, 
therefore, scents to he in the interest of constancy, not differentia- 
tion, and what poivcr it is that produces one sort of tissue from 
another, as must Jiappen in the developing embryo, is still a 
mystery. 

SECTION V — PHYSIOLOGICAL UNITS 

This difficulty has led to the assumption of some sort of phys- 
iological units, some of which are active at certain stages of 
development, others at other stages ; and the chromatin granules 
whose qualitative division is in most cases carefully insured 
are quite generally regarded as the repository of these units 
and the common vehicle of hereditary transmission. Such were 
the gemmules of Darwin,^ the stirp of Galton, the idioplasm of 
Nageli, and the determinants of Weismann."* 

1 Wilson, The Cell, pp. 1 16-12 1. - Ibid. p. 90. 

^ See Darwin, Animals and Plants, chap, xxvii. 

4 Weismann's elaborate theory of heredity regarded the germ plasm as the 
original substance, of which the body is the natural expansion. This " ancestral 
germ plasm " is unchanging, unchangeable, and, so long as the species endures, is 
immortal. He regards this germ plasm as comprised ultimately of "biophors" 
(life bearers), which may be spoken of as living molecules. These biophors, or 
ultimate units, are combined in an orderly manner into " determinants," whose 
activity at development determines what the particular part shall be. These 



THE MECHANISM OF DEVELOPMENT 153 

Whether or not any of these theories finally hold, this signifi- 
cant point remains, — that an adequate theory of heredity must 
account for the following facts : 

1. A single cell thrown off from the sexual parts of a mature 
individual will, under proper conditions, produce an entirely 
new individual in all essential respects like the parent, but in 
minor respects different. 

2. Commonly a cell or a number of cells taken from any 
other part of the body will wither and die, or, if growth follows, 
only one kind of tissue develops ; but in some instances (the 
begonia and others) the smallest bit of leaf, under favorable 
conditions, is able to grow and produce a new plant capable of 
bearing blossoms and seeds. ^ 

3. The mechanism of cell division seems admirably adapted 
to insuring growth without differentiation. 

4. But differentiation does take place, and in process of 
development a great variety of different cells arise from the 
single original germ cell. 

5. These "differentiations" take place at different but 
proper stages, insuring orderly arrangement and, for the most 
part, uniform results. 

6. There is always more or less variation between individuals, 
showing that the problem of development and inheritance is 
something else than absolute descent without change. 

We still seek, therefore, physical units with sufficiently exact 
properties to insure the general character of development, with 
such mutual relations as shall provide for orderly, not simultan- 
eous development, sufficiently elastic in their constitution (or 
combining powers) to admit of certain deviation, and each withal 
gifted with the power of nutrition, growth, and multiplication by 
division. Such in general are the properties of the physiological 

determinants are united into " ids," wliich are held to be identical with chromatin 
granules, and these in turn are assembled into " idants," which correspond with 
chromosomes. For a full explanation of Weismann's theory, see his Essays on 
Heredity, chap, iv, and his Germ Plasm, chap. i. 

^ It i.s a significant fact that if two begonia leaves be placed on sand simultane- 
ously, one taken from a plant just about to blossom, the other from one just past 
the blossoming period, the plant from the former will flower first. For Weismann's 
views, see his Essays on Heredity, chap. iv. 



154 CAUSES OF VARIATION 

units required to explain the function and achievements of the 
germ plasm, — the bit of vitalized matter that holds within its 
substance all the potentialities of its particular kind of life. 

Summary. The causes of variation are closely connected 
with the mechanism of growth and differentiation. The cell is 
the unit of structure and all growth is by cell division ; but it 
is not the unit of differentiation of different parts of the body, 
because all parts arise from one original cell, the germ cell. 

Cell division seems admirably adapted to insure absolute trans- 
mission without variability of any kind. But both differentiation 
and variability zxq facts. We seek, therefore, a "physiological 
unit" more minute than the cell, whose activities and possibly 
whose combinations with other physiological units of different 
properties are able to bring forth first differentiation within the 
body and later differences between different individuals. 

ADDITIONAL REFERENCES 

Chromosome Vesicles in Maturation. By \V. M. Smallwood. Science, 

XXI, 386. 
Cytological Features of Fertilization. By W. H. Blackman. 

Proceedings of the Royal Society, London, LXIII, 400-401. 
Fertility of Eggs after Removal of Cock. By L. G. Jarvis. 

Experiment Station Record, XI, 671. 
Laws of Embryonic Development : the Law of Von Baer. By 

Otto Glaser. Science, XV, 976-982. 
Mechanism of Development. By William Turner, F.R.S. Popular 

Science Monthly, LVII, 561-575. 
Ontogenetic and Phylogenetic Variation. By H. F. Osborn. 

Science, IV, 786-789. 
Problem of Development. By E. B. Wilson. Science, XXI, 281-293. 
Protoplasmic Structure. By E. B. Wilson. Science, II, 893-899; 

X, 33-45- 

Some Observations and Considerations upon Maturation Phe- 
nomena of Germ Cells. By T. H. Montgomery. Biological 
Bulletin, VI, 1904. 

Structure and Formation of Pus Cells. Experiment Station 
Record, XIV, 1016. 

Vitality of Pollen. (Roses, twenty-two days ; clivias, three months.) 
Experiment Station Record, XIII, 620; (Bear, thirty days) XV, 872. 



CHAPTER VIII 

INTERNAL CAUSES OF VARIATION 

While the causes of variation are both internal and external 
to the organism, the facts of the last chapter must satisfy 
the student of breeding problems that many of the processes 
attendant upon growth and reproduction are fruitful sources of 
variability. It is the purpose of the present chapter to discuss 
these internal influences somewhat at length. They are of two 
kinds, — (i) those affecting the individual only, and (2) those 
affecting the race as a whole. It is expedient to distinguish 
between these two classes, and the chapter will be divided into 
two parts, corresponding to these distinctions, as follows: (i) 
internal influences affecting primarily the individual ; (2) internal 
influences affecting: the race as a whole. 



I— INTERNAL INFLUENCES AFFECTING PRIMARILY 
THE INDIVIDUAL 

SECTION I — CELL DIVISION 

Growth is the result of cell division. Manifestly, therefore, 
all differences in size or in pattern are intimately dependent upon 
the extent and regularity of this process. 

Morphological variation due to cell division. Whatever influ- 
ences underlie the phenomena of mitosis, all questions of form 
or size are absolutely dependent upon the extent to which cell 
division and its attendant growth proceed. The individual cells 
in giants are not larger than those of normal specimens, but they 
are more numerous ; and in dwarfs they are not smaller, but 
fewer in number.^ What energies decide how far cell division 
shall proceed and when it shall stop in the case of each separate 

1 Wilson, The Cell, pp. 38S-389. 

155 



156 CAUSES OF VARIATION 

organ we do not know. Food and climate undoubtedly exert a 
general influence, as we shall see, but altogether aside from this 
there must be profound internal forces or interrelationships, 
upon the normal exercise of which all typical results depend. 

Consider the development of a normal individual from the 
fertilized ovum to maturity. The circumstances require not only 
that arm, leg, and bone, heart, liver, and brain, arise at the proper 
time and place, but also that the attendant cell divisions tji each 
proceed to the requisite number and then stop. If the number be 
too few, a dwarf is the result; if too large, a giant ; and if too 
few in some parts (arrested development) or too large in others 
(hypertrophy), the individual is thrown out of proportion and is 
recognized as more or less of a monstrosity according to the 
degree of disproportion. To be sure, all these things occasion- 
ally happen, and yet, in the majority of cases, the process of 
cell division is adjusted with a nicety that is nothing short of 
marvelous ; in any event, the results secured, though varying 
somewhat in total development, are yet almost absolutely 
proportional (^.)} 

Whatever may be the controlling force to decide at what point 
cell division in each case shall stop and when the individual as 
a whole shall cease to grow, the plain physiological fact is that 
all considerations of size (quantitative variation) are fundamen- 
tally those of cell division. 

The cessation of growth at maturity does not imply the loss 
of power of cell division, because most forms of life, plant or ani- 
mal, have more or less powers of regeneration if a part is lost 
or injured. If a leg of a salamander be cut away, it will speedily 
be restored, bones and all, as good as new. A tail of a lizard is 
readily broken off, separating not between two vertebrae but at 
the middle of a vertebra (in some species generally the seventh 
caudal). 2 When the tail regenerates, however, the vertebrae do 

1 At this point the author questions his own statement. As a matter of fact, 
the data involved have not been submitted to absokite mathematical determina- 
tion. We do not know whether the normal deviation in size due to variation in 
cell division is the same for all species ; nor do we know whether in giants and 
dwarfs all parts bear the same relative proportions as in normal specimens ; 
indeed, there is ground for believing that they do not. In the most general 
sense, however, the statement is true. 2 Morgan, Regeneration, p. 198. 



INTERNAL CAUSES OF VARIATION 157 

not regenerate, and in their place there is only a "cartilaginous 
tube attached to the broken vertebra." ^ 

In the first case (that of the salamander) cell division, which 
would normally remain suspended through life, was able upon 
occasion not only to resume activity but also to begin back at the 
proper point in ontogeny ^ and repeat its normal processes from 
that point onward. Moreover, in this particular instance it can 
do this not once but many times. ^ In the lizard, on the other 
hand, regeneration is not complete, as no true vertebrae are 
formed. Higher animals generally have but slight powers of 
regeneration, but all have enough to repair ordinary injuries to 
the skin, bone, nerves, etc., showing that the power of cell 
division is not entirely lost at maturity; in other words, that 
cessation of growth when the normal size is reached is due to 
some cause other than the failure of the power of cell division. 
There are many cases of abnormal size of certain parts due to a 
failure of this process to arrest itself at or near the proper 
point. "Big heads," "giant kidneys," and similar pathological 
cases are instances in point, but whether the division is mitotic 
or amitotic has not, so far as the writer is informed, been 
determined. 

While the limitation of cell division can certainly be influenced, 
especially by the food supply and by exercise, it is manifest that 
its absolute control is, and doubtless always will be, largely beyond 
our power. All animals get feed enough to more than build their 
bodies, and the point at which growth ceases seems to be mainly 
constitutional. If we could regulate size directly, it would vastly 
simplify the process of breeding, but as it is now, we are obliged 
to "breed for size " and feed accordingly. 

1 Morgan, Regeneration, p. 198. 

2 Ontogeny refers to the development of the mdividual, as phylogeny refers to 
that of the race. 

3 The absolute limits of regeneration are not known. Speaking generally, they 
are high in plants and low in animals. The salamander has been known, however, 
to restore tail and all four legs six successive times (Morgan, Regeneration, p. 5). 
The deer grows a new set of antlers every year. This is hardly a case of regener- 
ation, however, because successive growths are each more complicated than the 
former, each adding its characteristic prong; but it is a good instance to show the 
persistence of the power of cell division. 



158 CAUSES OF VARIATION 

Meristic variation in general due to cell division. All differen- 
tiation involving numbers of duplicate parts manifestly has its 
seat in cell division. An additional division at the point of origin 
of the series doubles the mmber, but an extra division at the 
point of origin of a member adds a pair, if both daughter cells 
develop, or a single member if but one develops. 

When the number in a meristic series is even the series is 
easily conceivable as having arisen from a corresponding number 
of cell divisions. For example : 

2 in the series, i division 

4 in the series, 2 divisions 

6 in the series, 2 divisions, with one pair dividing again 

8 in the series, 3 divisions 

10 in the series, 3 divisions, with one pair dividing again 

If the number of members is odd, it is only necessary to assume 
that one of the even numbers failed to develop, or, what is more 
likely, that one of a pair indulges in additional division, — its 
sister member remaining single ; thus : 

3 members, i division, one member dividing again 

5 members, 2 divisions, one member dividing again 

7 members, 2 divisions, two members dividing again 

9 members, 3 divisions, one member dividing again 

The frequent recurrence of five as a digital number is one of 
the mysteries in creation, and its singular persistence is another. 
It is, however, subject to many deviations, as was seen in the 
chapter on "Meristic Variation"; even in the rose family there 
is an occasional loss of one of the members. 

The frequent presence of six digits is not to be explained by 
reversion, as nobody supposes that number ever to have been 
characteristic in any species, — a fact that should be noted by 
some of our friends who are always ready to invoke the aid of 
atavism to explain every abnormality. 

Meristic variation, like other deviations arising from external 
causes, is to some extent hereditary, and capable of being in- 
fluenced, if not absolutely controlled, through selection. No 
other method is known, aside from the fact that external injury 



INTERNAL CAUSES OF VARIATION 159 

to many plants and certain animals results in budding and mul- 
tiplication of parts. We cut the main stem of a small tree or 
shrub in order to increase the number of side branches. Some- 
what similarly, injured parts are often doubled in regeneration.^ 
In this way lizards may be made to produce an increased number 
of toes and even double feet, legs, and tail. It is supposed that 
double feet, sometimes seen even in mammals, may be produced 
by a "fold of the amnion constricting the middle of the begin- 
ning of the young leg " ^ in the embryo. This, however, is curi- 
ous rather than valuable to us, as it tends to explain abnormalities 
rather than to point a way to practical improvement. 

Irregularities in cell division a cause of variation.-^ The char- 
acteristic act in cell division seems to be the splitting of the 
chromosomes (or chromatin granules) and the migration of exact 
equivalents to each new daughter cell, strongly suggesting that 
the assortment of " physiological units " (whatever they may be) 
received by one daughter cell is an exact duplicate of that received 
by the other, thus insuring an orderly and systematic develop- 
ment through a strictly qualitative division of hereditary sub- 
stance at each and every stage of growth. 

The whole mechanism of mitosis seems adjusted to this end, 
and if the assumption is true its significance can hardly be over- 
estimated. If this careful adjustment of the mechanism of cell 
division is necessary to orderly development, it is manifest that 
any substantial deviation is likely, if not certain, to result in 
variation more or less profound. Such deviation is characteristic 
of amitotic division generally, and it is more than conceivable 
that the ordinary process is subject to occasional " slips." Some 
chromatin granule may fail to divide at the proper moment and 
may pass over to one daughter cell entire,* or, conversely, it 
may indulge in an extra division. Substantial deviations in the 
process are known to occur not rarely but frequently. For ex- 
ample, the splitting sometimes takes place in the spireme stage, 
sometimes after the formation of the chromosomes ; sometimes 

1 Morgan, Regeneration, pp. 137-139. 

2 Ibid. p. 139. 

^ See previous cliapter. 

4 This is known to occur in certain instances in maturation. 



l6o CAUSES OF VARIATION 

the centrosomc divides before the resting stage, more commonly 
afterward. Taking it ah in all, here is an exceedingly compli- 
cated procedure, only semi-mechanical and therefore subject to 
deviations. Absolute constancy demands no failure in the final 
object of exact qualitative division, but the student sees many 
possibilities for unequal division and therefore for deviation in 
growth. Is this the fundamental cause of mutations ? One thing 
is certain, — living forms are made up of elements, and these 
elements are subject to strange combinations throughout the 
entire range of plant and animal life, and the facts seem to teach 
that from time to time combinations may arise that are entirely 
new. Moreover, whole units seem occasionally to be " lost out," 
as when horned cattle suddenly give rise to polled strains, hairy 
species to smooth varieties, colored to albino, etc. 

Conversely, do vital elements like chemical radicles assume 
new combinations from time to time, giving rise to new char- 
acters and new types which we call " mutants " .'' We do not 
know, and yet we feel the conviction that at this point we are 
very close to the "origin of characters," the cause of mutations 
and of variation in general. 

Manifestly, in so far as irregularities in cell division may be a 
cause of variation, the matter lies absolutely beyond our control 
except that lines in which it is believed to occur may be avoided 
in selection. Here is a field, however, too far beyond our pres- 
ent knowledge to admit of anything more than the merest 
mention. We confidently believe that the future will shed more 
light on this obscure subject. 



SECTION II— BISEXUAL REPRODUCTION A FUNDAMENTAL 
CAUSE OF VARIATION 

Among higher animals and plants the new individual is the 
direct product of two others, — the male and the female parent, 
— and is of necessity different from either, being a product of 
both. In bisexual reproduction, therefore, biologists recognize a 
fundamental cause of variation, — slight if the parents are of like 
blood lines, extreme if of radically different, as in hybridism. 



INTERNAL CAUSES OF VARIATION i6l 

This view of the case is borne out by the facts of fecundation 
or fertilization of the ovum, which may be briefly described as 
follows : ^ 

The ovum. This is the finished product of the sexual cells of 
the mother parent, and consists of a nucleus with its characteristic 
chromatin granules surrounded by a comparatively large mass of 
cytoplasm. 

The sperm cell. This is the finished product of the sexual cells 
of the male parent. It is called a spermatozoon in animals, sper- 
matozoid in lower plants, and pollen grain in higher plants. It 
is in all cases vastly smaller than the corresponding ovum, being 
almost destitute of cytoplasm. The characteristic elements of 
the ovum are its nucleus and the cytoplasm, while the character- 
istic elements of the spermatozoon are its nucleus, borne in the 
"head," and a centrosome, generally carried in the "middle 
piece." The tail, formed from the small amount of cytoplasm, 
seems to have no function beyond providing motile power, and is 
absent in the pollen of higher plants. 

Fertilization. Both the ovum and the sperm cell have arisen 
in their respective organs by the method of cell division, display- 
ing in the process the ordinary phenomena of mitosis.'^ But 
both have reached the end of their powers of self-division, and if 
left alone they will be thrown off from their respective points of 
origin to wither and die. 

If, however, they are brought near together, mutual attraction 
ensues, the spermatozoon (or other sperm cell) enters the ovum, 
the nuclei approach each other and fuse, the centrosome divides, 
an amphiaster is formed, and cell division ensues. The ovum is 
now fertilized, segmentation proceeds, and a new individual is 
established in an independent existence. 

The new individual is thus the possessor of actual living mat- 
ter (physiological units) derived from both parents, and thus 
inherits literally the substance of both, having come into direct 
possession of material identical with the living matter of both 
parents. 

^ For a fuller discussion of this subject, see Wilson, The Cell, pp. 178-231. 
' For a brief statement of what is involved in maturation, see the next 
section. 



1 62 CAUSES OF VARIATION 

All that is involvctl in fertilization is not well understood, but 
its essential feature is the jtnio)i or fusion of the jutclcar matter 
{clironiosovies) of the germ cells from tivo parents to form the 
cleavage or segmentation nucleus whose subseqiient groivtJi and 
divisions '^ give rise to all the nuclei of the body.'' This fertilized 
ovum becomes, therefore, the first cell of the new being, which 
inherits directly and equally a portion of the nuclear matter from 
both parents, so that " every nucleus of the child may contain 
nuclear substance derived from both parents." ^ Here, then, is 
the avenue of all inheritance, and, as the new individual is a kind 
of blend of both parents, we see in fertilization an initial and 
primary cause of variation. 

This is the only form of variation recognized by Weismann in 
his earlier writings as in any sense hereditary. All deviations 
in development due to external causes were conceived to affect 
the body (soma plasm ^) only, exerting no influence upon the 
ancestral germ plasm .'^ True, he later announced the theory of 
germinal selection, in which a kind of struggle for existence is 
conceived as taking place between the "biophors " (physiological 
units), by which some prosper and multiply exceedingly while 
others are crowded out entirely.* This would give another cause 
of variation within the germ plasm of each individual. 

Biologists generally recognize internal causes of variation 
other than these, and yet this union of the chromosomes from 
different individuals taking place at each new generation must be 
regarded as a very effective means of introducing variability. 
Even if the offspring of a single parent, as in parthenogenesis, 
should be an exact duplicate of the parent, — which it is not, — 
every one would recognize the fact that the blending of heredi- 
tary substance from two parents must of necessity produce an 
individual with a new combination of faculties. 

It is a variation, however, confined not only to the characters 
of the race but also to the family possessions of the particular 
parents. Bisexual reproduction cannot be looked upon as a means 

1 Wilson, The Cell, p. 182. 

2 " Soma plasm " is a term used to represent the protoplasms of the body in 
general as distinct from the output of the sexual cells (germ plasm). 

2 Weismann, The Germ Plasm, chap. ix. 

* Weismann, Germinal Selection (pamphlet). 



INTERNAL CAUSES OF VARIATION 163 

of introducing new characters into the race, and while it is mani- 
festly a fruitful source of never-ending combinations of racial 
characters in new individuals, yet variations so introduced are 
comparatively slight except when the two parents belong to sepa- 
rate lines. 

Fertilization of the ovum is something more than a stimulus 
to growth. It is a real union of material bodies, physiological 
units, or whatever they may be called, representing the hereditary 
substance of both parents. Bisexual reproduction is therefore 
not only a guaranty of transmission of racial characters but also 
an assurance of inheritance with some variation. 

Control. Here is a fundamental cause of variation practically 
under the control of the breeder through selection. True, his 
knowledge and his judgment are insufficient to insure him against 
mistakes in mating, and it is also true that there are many other 
influences at work to produce variations, but this is the field in 
which the breeder can exert the largest influence, and it is by 
selection that the greatest results in improvement have been 
attained up to date. 

Sexual selection, 1 preferential mating,- and assortative mating.'^ 
Powerful as are these influences in directing the trend of varia- 
bility, they yet belong to general evolution because they are ele- 
ments in natural selection, and they have no place in the present 
discussion. 

SECTION III — MATURATION AND THE REDUCTION OF 
THE CHROMOSOMES A CAUSE OF VARIATION 

Fertilization is a process whose inevitable consequence would 
seem to be the ^^ piling tip " of nuclear matter indefitiitely ; for 
if, with each new generation, the chromosomes (or physiological 
units) of the one parent are added to those of the other, it would 
seem that in time the resulting nuclear matter would speedily 
become " unmanageably large " and inconceivably complex, — an 
event certain to follow except for a series of very remarkable 

1 Darwin, Origin of Species, see Index. 

2 Pearson, Grammar of Science, pp. 425-428. 

3 Ibid. pp. 4^9-437- 



1 64 CAUSES OF VARIATION 

facts occurring just previous to fertilization and by which tJie 
mimber of cJiroinosomes in both the male and female germ cells is 
reduced to one half the nsnal or sojnatic number, so that their 
union at fertiHzation restores the true number of chromosomes 
typical of the race. Thus, if the somatic number of chromosomes 
is sixteen, the number in the germ cells at fertilization will be 
eight each, or sixteen after fusion of the nuclei. This process by 
which the number of chromosomes is halved in the germ cell is 
known as reduction, and is supposed to be the significant feature 
of the maturation process by which the male and female germ 
cells are prepared for union. 

Parallelism in the sexes. Maturation and its attendant phe- 
nomena of reduction in the number of chromosomes is a subject 
that must be considered separately in the male and the female, 
and yet there exists a strange parallelism worthy of notice. To 
quote Wilson ^ : 

Recent research has shown that maturation conforms to the same type 
in both sexes. . . . Stated in the most general terms this parallel is as fol- 
lows: In both sexes the final reduction in the number of chromosomes is 
effected in the course of the last two cell divisions, or jiiaturatioii dii'isions 
[as they are called], by which the definitive germ cells arise, each of the 
four cells thus formed having but half the usual number of chromosomes. 
In the female but one of the four cells [resulting from the two maturation 
divisions] forms the ovum proper, while the other three, known as the 
polar bodies^ are minute, rudimentary, and incapable of development. In 
the male, on the other hand, all four of the cells become functional sper- 
matozoa. This difference between the two sexes is probal:)ly due to the 
physiological division of labor between the germ cells, the spermatozoa 
being motile and very small, while the egg contains a large amount of 
protoplasm and yolk, out of which the main mass of the embryonic body is 
formed. In the male, therefore, all of the four cells may '^ become func- 
tional ; in the female the functions of development have become restricted 
to but one of the four, while the others have become rudimentary. 

1 Wilson, The Cell, p. 234. 

2 The author is here speaking specifically of reproduction in animals, as 
plants do not form polar bodies. The difference in plant and animal reproduc- 
tion is, however, more in form than in significance. 

^ The author says " may " become functional. He means by this that each of 
the four cells (spermatozoa) arising from the last two divisions is capable of 
fertilizing an ovum, while of the four cells arising from the last two divisions in 
the female only one is capable of being fertilized. 



INTERNAL CAUSES OF VARIATION 165 

Maturation and reduction in animals and in plants radically- 
different. This process is far better understood in animals than 
in plants, and in many respects it is radically different in the 
two. It is simpler in animals and more direct. In them the last 
two cell divisions always (apparently) give rise in the male to 
four functional spermatozoa, but in the female to one functional 
cell, retaining nearly all the cytoplasm, and to three polar bodies 
incapable of fertilization and destined to wither away and disap- 
pear. The same general facts seem to hold for animals of all 
species, and Wilson remarks ^ : 

The evidence is steadily accumulating that reduction is accomplished 
b)' two maturation divisions throughout the animal kingdom, even in the 
unicellular forms ; though in certain Infusoria an additional division occurs, 
while in some other Protozoa only one maturation division has thus far 
been made out. 

Among plants, also, two maturation divisions occur in all the higher 
forms, and in some at least of the lower ones. Here, however, the phe- 
nomena are complicated by the fact that the two divisions do not, as a rule, 
give rise directly to the four sexual germ cells, but to asexual .spores which 
undergo additional divisions before the definitive germ cells are produced.- 
[The end product, however, shows the same reduction in the number of 
chromosomes.] 

A brief description of reduction in animals is worth consider- 
ing somewhat in detail, as it is fairly well known and cannot 
fail to impress the student with its fundamental significance and 
the nicety of adjustment of the mechanism of living processes. 

Reduction in the female.-^ Among animals the production of 
the female germ cell (the ovum) is the special function of the 
ovaries. In the tissues of these organs cell division proceeds 
under the usual mitotic plan, giving rise to a series of cells 
known as oogonia. At a certain point mitotic division halts, and 
each cell prepares for the final (maturation) changes. Food 
material is absorbed, the cytoplasm increases in bulk, the nucleus 
greatly enlarges, and the cell, now known as an oocyte^ is ready 

1 Wilson, The Cell, p. 235. 

2 Ibid. pp. 235-236. Note that, in general, polar bodies are not formed in 
plants. 

3 Ibid. pp. 236-240. This description applies to the animal. The details are 
distinctly different in plants, to be discussed later. 



1 66 CAUSES OF VARIATION 

for the last two, or maturation, divisions. In this condition the 
egg cell remains until near the time of fertilization, when the 
process of maturation proper takes place. 

The significant details of this interesting series of changes are 
concerned with the nucleus and are substantially as follows : 
During the long resting stage preparatory to these final divisions 
the nucleus increases in bulk and the chromatin matter assumes 
the reticular form characteristic of the resting stage of dividing 
cells in general. In this condition the nucleus is known as the 
"germinal vesicle." Up to this point the number of chromo- 
somes is the same as that of the body cells in general. Their 
identity is, of course, now lost, but as the time for the first 
maturation division arrives, instead of the spireme of ordinary 
mitosis breaking up into the usual number of chromosomes, 
there appear more or less spontaneously a number of " primary 
chromatin masses " in the form of rods, rings, or V-shaped bodies, 
each of which ultimately breaks up into four smaller bodies. 
These groups of four are always one Jialf the Jisnal or somatic 
number of chromosomes. 

Whether the chromatin masses appear in the form of rods, 
rings, or otherwise, the final result seems to be always the same ; 
namely, the breaking up of each into four smaller bodies, either 
by two longitudinal divisiojts or by one (the first) longitudinal 
and one transverse. The details differ in different species and 
have been worked out in but few cases. It is not important 
here to trace the bewildering differences, but rather to describe 
typical behavior.^ 

Having assumed this condition the nucleus now migrates to 
the margin of the cell, each of the groups of four (tetrads in rod- 
shaped cases) splitting into two smaller groups of two each 
(dyads). ^ The mass now divides, one pair from each group 

1 For a full discussion of the different forms of reduction, see Wilson, The 
Cell, V, 233-287. 

2 The terms " tetrad " and " dyad " of course apply only in the case of rod- 
shaped masses. In the case of rings (common in animals) and V-shaped masses 
(common in plants) the parting into four takes place gradually as the work pro- 
ceeds, while in the case of rods the division into four takes place early and the 
parts are distinct from the first. In this formation the two divisions take place 
much more rapidly than in the case of rings, which split and divide slowly. The 



INTERNAL CAUSES OF VARIATION 167 

remaining in the cell, the other passing outside, forming the 
first polar body, which may or may not undergo further division. 

The portion now remaining within the cell consists of groups 
of two each, instead of four, and their number is of course the 
same as before, namely, one half the somatic number of chromo- 
somes. Immediately now, without assuming the resting stage, 
the dyads, or groups of twos, turn one fourth around, taking a 
position at right angles to the margin of the cell, and (7^ oiice 
divide again, one member of each pair remaining behind iti the 
egg eel I, the other passing ont, forming the second pohxr body. 

The first polar body carried away one half the nuclear matter, 
and the remaining half has now been divided equally between 
the second polar body and the main cell, which is now ready for 
fertilization and is from this time on spoken of as the ovum. 

Neither polar body carries any appreciable quantity of cyto- 
plasm, and both are destined to degenerate and disappear. The 
first one, however, containing half of the total nuclear matter, 
commonly divides once, so that the first polar body represents 
not one, but two cells, — the first and the third polar bodies. 

The total result, then, of this complicated process seems to 
be the equal division of the chromatin matter between the 
ovum, capable of fertilization, and three polar bodies, destined 
to extinction. 

A group of four cells thus arises, - — namely, the mature ^gg 
(ovum), which after fertilization gives rise to the embryo, and 
three small cells or polar bodies (incapable of fertilization),^ 
which take no part in the further development, are discarded, 
and soon die without further change. The Q.gg nucleus (of the 
ovum proper) is now ready for union with the sperm nucleus,^ 
which process is known as fertilization. 

*' In some cases — for example in the sea urchin — the polar 
bodies are formed before fertilization, while the o^gg is still in 

tetrad form is always chosen for description because the details are capable of 
more definite statement. Whatever the form of the masses, however, the final 
result seems always the same ; namely, a reduction to one half the usual number 
of chromosomes, and this by the method of division and extrusion. 

1 In rare instances the polar bodies have commenced to segment, but they 
never proceed far in development. 

2 Wilson, The Cell, pp. 236-237. 




Fig. 24. Diagrams showing (lie essential-facts in the iiiaturatinn of the egg. 
The somatic number of chromosomes is supposed to be four 

A, initial pliase: two tetrads have been formed in the germinal vescicle. B. the two 
tetrads have been drawn up about the spindle to form the equatorial plate of the (irst 
polar mitotic figure. C, the mitotic figure has rotated into position, leaving the remains 
of the germinal vesicle at g.v. D, formation of the first polar body : each tetrad 
divides into two dyads. E, first polar body formed: two dyads in it and also in the 
egg (/•/'.'). F. preparation for the second division. (7, second polar body forming and the 
first dividing: each dyad divides into two single chromosomes. //, final result: tliree 
polar biidies and the mature ovum, eacli containing two single chromosomes, or half 
the somatic number ; c; the egg centrosome, which now degenerates and is lost. — After 
Wilson 

168 



INTERNAL CAUSES OF VARIATION 169 

the ovary. More commonly, as in annelids, gasteropods, and 
nematodes, they are not formed until after the spermatozoon 
has made its entrance ; while in a few cases one polar body 
may be formed before fertilization and one afterward, as in the 
lamprey eel, the frog, and in Ainphioxus. In all these cases 
the essential j^henomena are the same. Two minvite cells are 
formed, one after the other, in rajiid succession and near the 
upper or animal pole of the ovum ; and in many cases the first 
of these divides into two as the second is formed." 

To what extent this division is qualitative is unknown. Of 
one thing we are certain : soincwJicrc in the process the nuviber 
of eJiroDiosouies Jias been reduced to exactly one half the number 
characteristic of the species. 

It was formerly supposed by Van Beneden, Weismann, and 
Boveri that reduction consists in the casting out and degenera- 
tion of half of the chromosomes. " Later researches conclusively 
showed, however, that this view cannot be sustained, and that 
reduction is effected by a rearrani^emoit and rcdistribjition of the 
nuclear substance, without loss of any of its essential constitu- 
ents." ^ This is said because the groups — tetrads, rods, rings, 
etc. — arise spontaneously in the nucleus in the reduced number. 
The loss occurs later in the extrusion of the polar bodies, but 
no corresponding loss takes place on the male side because all 
four cells are functional, though not all alike. 

Reduction in the male.- The maturation j^rocesses in the male 
and female are i)ractically identical in their results, with two 
exceptions; namely, first, in the male the four cells resulting 
from the maturation divisions are all alike and all functional, and 
second, they are exceedingly small in size as compared with the 
ovum, being almost destitute of cytoplasm. 

The spermatogonia, corresponding to the oogonia of the 
female, arise in the testes by mitotic division, with the full 
somatic number of chromosomes. As in the female, they reach 
a stage where division ceases for a time and enlargement ensues, 
in which condition the cells are known as spermatocytes (corre- 
sponding to oocytes in the female). 

1 Wilson, The Cell, p. 233. 
- Ibid. pp. 241-242, 



170 



CAUSES OF VARIATION 



At the proper stage each spermatocyte undergoes two divi- 
sions (maturation divisions) into four cells, called spermatids, 
each of which develops a tail and becomes functional, in which 
finished condition it is known as a spermatozoon, when it is 
ready to enter and fertilize the ripened ovum. 

The history and distribution of the chromatin matter in the 
male is identical with that in the female, so that each sperma- 
tozoon inherits one foiirtJi the chromatin matter and one half the 
chromosomes of the original cell. In plants the process differs 
but the general results are the same. 

Significance of reduction. On the female side three fourths of 
the chromatin matter has been extruded in the polar bodies, and 
therefore lost to the line of descent. Whether reduction takes 
place by extrusion or by rearrangement, one thing is certain : 
when the second division is transverse, and possibly when it is 
longitudinal, it results in an unequal division of physiological 
nnits, if the identity of the chromosomes and the chromatin 
granules has any meaning. If this division be anything else 
than strictly qualitative, then the extrusion of the polar bodies 
means a loss of something qualitative on the female side. 

On the male side the loss is not absolute, because all four 
cells are functional, but if reduction has the meaning we attach 
to it, these four spermatozoa are not identical but different in 
the hereditary substance with which they are provided. 

Significance of fertilization. Here, then, are two sexual cells 
ready for union. Each has lost large portions of its chromatin 
matter, the evident vehicle of transmission, and each brings to 
the union but one half the number of chromosomes characteris- 
tic of its species, strongly suggesting a loss of certain chromatin 
granules and the hereditary qualities they represented. 

When fusion of the nuclei of these two germ cells takes place 
at fertilization, however, the act of union again restores the full 
and proper number of chromosomes, which will remain charac- 
teristic of the new individual throughout its life, and which it 
will hand down to posterity, always through the same compli- 
cated method we have attempted to describe. The number of 
chromosomes is evidently kept constant by the complicated 
process of reduction during maturation and by fertilization 



INTERNAL CAUSES OF VARIATION 171 

afterward ; but what about their character ? In what condition 
have they emerged from this seemingly incomprehensible tangle ? 
Is nature as careful to preserve their quality as it is their number ? 

What opportunities for profound variation ! Certainly if 
chromatin matter has any fundamental meaning, and if chromo- 
somes are in any way representative of physiological units, 
and if they in their turn are in any way representative of racial 
characters, these processes must have some meaning in varia- 
tion. Certainly we have been very near in all this to the material 
basis of transmission of racial characters, and to fundamental and 
initial causes of variation. 

Something has been lost in the two peculiar divisions attend- 
ing maturation. Some definite groupings of hereditary substance 
have disappeared from the line of descent. They could not have 
represented, ordinarily, definite portions of a body, but they must 
represent something. What chances for accident ! And, in the 
light of these marvelous phenomena, do we wonder that individ- 
uals are sometimes born minus a leg, an arm, or some other part .? 
Do we wonder that vital parts are so often affected, and that one 
third of our children die in infancy ? How many die before birth, 
and how many more die at some stage in embryo ! 

Evidently all that is required to make a living being is a 
fairly perfect development of the vital parts ^ quite regardless of 
the presence or absence of the many other racial characters 
that should be present in the perfect individual. Is it surprising 
that perfect individuals are so few, and that defectives are 
frequently so far from the type ? Here is material for study 
on the part of criminologists and courts of justice, as well as 
students of methods of economic improvement. 

Reduction and fertilization in plants. It may be said in 
general that in animals the evidence tends to the assumption 
that reduction takes place at the extrusion of the second polar 
body ; that each group (rod, ring, or V-shaped body) is in reality 
a doubled (bivalent) chromosome, and that the first polar body 
removes one half of each (split) chromosome, while the next 
removes every alternate chromosome. 

While the facts of reduction in plants are yet in a hopeless 
tangle, it is safe to say that the evidence tends to show that no 



172 



CAUSES OF VARIATION 



true polar bodies are formed,^ but that the chromosomes sud- 
denly appear in reduced number at the first division, as if it 
were effected directly by the segmentation of the spireme 
thread (of the maturing germ cell) into half the somatic number 
of chromosomes. 

While details vary greatly, botanists recognize two stages in 
the development of the female germ cell of the plant, neither 
of which is identical with maturation in animals, though the first 
is fairly comparable thereto. The first stage, or sporogenesis, 
follows after that active massing of food material which marks in 
both plant and animal the preparation for reduction. At this 
time the nucleus divides quickly into four daughter nuclei, each 
of which is supplied with half the number of chromosomes that 
characterizes the species. The precise methods followed out are 
matters of much dispute among botanists, but the significant 
fact is that reduction is accomplished at this stage. 

Of these four daughter nuclei none are extruded, but three 
of them degenerate in the cytoplasm, while the fourth increases 
in size to form the embryo sac, which, without waiting for ferti- 
lization as among animals, continues to divide, — commonly 
twice, — giving rise to eight sub-nuclei, which arrange them- 
selves in definite positions. Two of these sub-nuclei remain 
near the center of the embryo sac and give rise to the endo- 
sperm ; three migrate to the extremity nearest the point of 
attachment with the pistil, and one of these (and one only) — 
the so-called egg nucleus — unites with the nucleus of the 
pollen grain to form the fertilized germ ; the three remaining 
migrate to the other extremity of the embryo sac and concern 
themselves with establishing a food supply with the parent plant. 

On the male side the process is simpler. The pollen nucleus 
divides, one half forming the pollen tube, along which the other 
half travels, dividing again at some point before uniting with the 
egg nucleus of the embryo sac. These divisions are evidently 
reducing divisions, as the pollen-grain nucleus brings to the 
union a reduced number of chromosomes. 

1 Disputed by Chamberlain, who believes that "the egg with its three polar 
bodies constitutes a generation directly comparable with the gametophytic genera- 
tion in plants." See Botanical Gazette^ XXXIX, 139; see also under " Xenia," in 
this text. 



INTERNAL CAUSES OF VARIATION 173 

Thus, while the plan is different in plants and in animals, the 
first stage, sporogenesis, in plants seems fully comparable with 
maturation in animals, and the same general end is accomplished. ^ 

After all, the manner of division is primarily of interest to 
the physiologist and does not concern us. Our interest is in 
the fact that maturation in general involves an actual loss of 
chromatin matter (hereditary substance) and a reduction in the 
number of chromosomes, and consequently of physiological units. 
In the present state of knowledge it seems safe to assume that 
both these results follow, whatever the mechanism of maturation 
in each particular instance. If this be true, here is a fertile and 
initial cause of profound variation, an excellent opportunity for 
losing important elements of the physical make-up, but, so far 
as we can see, no chance for positive gain, unless it be by new 
combinations, because nothing is introduced. 

Phenomena such as these are remarkable for what they sug- 
gest rather than for conclusions that can be positively drawn. 
The suggestion is that of substantial deviation in the very fun- 
damental process of transmission of the hereditary substance, — 
a deviation that cannot but be fruitful of variation in resulting 
individuals. 

Weismann's prediction. It is noteworthy that reduction was 
predicted by Weismann on purely theoretical grounds some 
years before it was known as a fact.^ He argued for its recur- 
rence as a physiological necessity to prevent the piling up of 
"ancestral idioplasm," — the physiological units to which he 
afterward gave the name of "ancestral units," '^ — and later 
developed the intricate system of biophors,"* determinants,^ ids,^ 
and idants,'^ by virtue of which he explained the constitution of 
the germ plasm," and which he used as the basis for his famous 
theories of heredity.^ 

1 For full discussion, see articles by B. M. Davis, Amcricait A'atiiraiist, XXXIX, 
Nos. 460 and 463. 

■^ Weismann, Essays on Heredity, I, 357, 363-396; II, 1 14-150; also Weis- 
mann, The Germ Plasm, chap. viii. ^ Weismann, Essays on Heredity, II, 116. 

* Weismann, The Germ Plasm, pp. 40-53. * Ibid. pp. 53-60. 

6 Weismann, Essays on Heredity, II, 136-138; Weismann, The Germ Plasm, 
pp. 60-75. 

" Weismann, The Germ Plasm, chap, i, pp. 37-85. 

^ Ibid. chap, ix, pp. 253-293. 



1 74 CAUSES OF VARIATION 

The later discovery of the mechanism of maturation and of 
the extrusion of the polar bodies was a startUng confirmation of 
Weismann's prediction, and went far to fix his theories of hered- 
ity in the minds of many biologists. In this connection Wilson 
very pertinently remarks : ^ 

The fulfillment of Weismann's prediction is one of the most interesting 
) esults of recent cytological research. It has been demonstrated in a manner 
which seems to be incontrovertible that the reducing divisions postulated 
by Weismann actually occur, though not precisely in the manner conceived 
by him, . . . but it remains quite an open question whether they have the 
significance attributed to them by Weismann. 

Just when the reduction occurs is not known. It was at first 
assumed that it occurs in connection with the extrusion of the 
second polar body, — an assumption based upon the development 
of parthenogenetic eggs. But plants do not form polar bodies, 
and again there is great uncertainty as to whether the rods 
(tetrads), rings, or V-shaped bodies (whose number is half the 
usual number of chromosomes) are to be regarded as represent- 
ing the usual number of chromosomes split and arranged in 
pairs, — in which case the second polar body would accomplish 
the reduction ; or whether the chromosomes as formerly known 
never emerge from the nucleus of the oocyte, so that the iden- 
tity of the chromosomes is in some way lost and the reduction 
is effected at this early stage by some sort of internal fusing, or 
perhaps by an entire rearrangement of chromatin granules. On 
this point the evidence is confusing, but on two significant 
points there is no doubt, — the loss of chromatin matter out of 
the line of descent, and a reduction of the chromosomes in the 
germ cells to one half the somatic number.^ 

Composition of the chromosomes.'^ In view of the important 
office of the chromosomes and the many theories of heredity 
based upon their nature and constitution, in view also of their 
evident importance in all studies on inheritance and variation, 

1 Wilson, The Cell, p. 246. 

2 By "somatic" number is meant the number characteristic of the soma,—' 
the body in general as distinct from the germinal matter whose function is not 
growth but reproduction. 

3 Wilson, The Cell, pp. 294-304. 



INTERNAL CAUSES OF VARIATION 175 

it may be well to note the substance of what is really known 
about their actual constitution. 

That they are not masses of homogeneous matter is certain, 
and that they consist of numbers of small granules capable of 
multiplication and division seems equally certain. To quote 
Wilson : 

The facts are now well established (i) that in a large number of cases 
the chromatin thread consists of a series of granules (chromosomes) 
imbedded in and held together by the linin substance ; (2) that the split- 
ting of the chromosomes is caused by the division of these more elementary 
bodies ; (3) that the chromatin grains may divide at the time when the 
spireme is only just beginning to emerge from the reticulum or resting 
stage. 

Because of these facts there arises the strongest tendency to 
attach individuality to the chromatin granules and to conceive 
them as built up of definite, though often diverse, physiological 
units, thus constituting a semi-mechanical basis for heredity, and 
incidentally for variation as well. This assumption Weismann 
and others have made. Whether the facts should be pushed to 
this extreme interpretation is, in the opinion of the author, as 
yet uncertain. The facts are extremely suggestive, to say the 
least, and it is certainly not too much to believe that at this 
point we have touched the physical basis of life and in some 
fashion the very root of inheritance and variation ; indeed we 
may proceed upon the conviction that transmission is a function 
of the chromatin granules. 

Reduction as a cause of variation. The most remarkable and 
suggestive fact about living beings is the numerical constancy 
of chromatin units (chromosomes) for each species, and the 
most remarkable and suggestive of all the vital processes is 
their reduction before fertilization. If, as we suppose, the 
chromosomes are the physical basis of inheritance, then in the 
loss of c1iroinati7i matter at maturation lies a fundamental cause 
of variatiofi, and one quite independent of the effects of fertili- 
zation afterward. 

Reduction would seem to be a process calculated to insure 
that no two germ cells, even from the same individual, should 
ever be alike, and this is the most evident reason for the 



176 CAUSKS OK VARIATION 

essential differences in children of the same parents, even in 
the case of twins.' 

It is true, of course, that no two individuals, even twins, can 
be developed under conditions of life exactly identical ; and yet 
the differences of condition cannot account for the fact that, 
while one brother resembles his father, another may resemble 

1 Twins are considered as arising from separate ova, as in the case of multiple 
births (pigs, dogs, etc.), and, of course, as exhibiting the deviations to be expected 
from different germs and distinct fertilization, as in litters generally. 

Some twins, however, are so nearly alike (identical twins) as to suggest the 
possibility of their having arisen from a single ovum in some way sejxirated into 
halves at its first cleavage, each half developing an individual. This view is 
evidently favored by Geddes and Thom.son (see The Evolution of Sex, p. 41). 

If twins should be developed in this manner, they would evidently be of the 
nearest possible similarity, for they represent but one ovum and but a single 
fertilization. 

This possibility is supported by the experiments of Roux, Endres, and Walter, 
in which each blastomere of the two-cell stage of the frog sometimes (not always) 
is capable of developing into a perfect individual. Driesch, working with echino- 
derms, established the same facts, which are also well known in the case of 
Amphioxus (see Wilson, The Cell, p. 419). 

Conversely, when two fertilized ova of sea urchin, or Ascari.s, adhere acci- 
dentally, they may develop into an embryo of unusual dimensions (see Loeb, 
Studies in General Physiology, Part II, p. 676). 

When, however, the blastomeres are not separated, but one of them is killed 
by a heated needle (Roux), the uninjured half alone develops, but it produces 
at the best a kind of half larva (right or left half), "containing one medullary 
fold, one auditory pit " (Wilson, The Cell, p. 399). Chun, Driesch, Morgan, and 
Fischel, working with ctenophore eggs, however, found that isolated blastomeres 
of the two-, four-, or eight-cell stages developed " defective larvae, having only 
four, two, or one row of swimming plates." Also " Crampton found that in the 
case of the marine gasteropod Jlynnnssa isolated blastomeres of two-cell or four- 
cell stages segmented exactly as if forming part of an entire embryo, and gave rise 
\.o fragments of a lawa, not to complete dwarfs as in the echinoderm" (Wilson, 
The Cell, p. 419). This attempt to form entire individuals from a portion only 
of a fertilized egg, resulting as it often does in dwarfs, seems to the writer a 
process closely akin to regeneration (which see in chapter on " Relative Stability 
and Instability of Living Matter"), and would seem to raise doubts as to its 
successful occurrence in the higher animals. 

Though not bearing especially upon the point in question, the matter of twins 
in cattle is unique and worthy of mention. Three kinds of twins are known in 
cattle: " (i) the twins may be both female and both normal; or (2) the sexes 
may be different and normal ; or (3) both may be males, in which case one always 
exhibits the peculiar abnormality known as a ' free-martin,' — the internal organs 
are male, but the external accessory organs are female, and there are also rudi- 
mentary female ducts" (Geddes and Thomson, The Evolution of Sex, p. 41). 
This is a kind of hermaphroditism, and not, as is commonly supposed, "a heifer 
twin with a bull." 



INTERNAL CAUSES OF VARIATION 177 

his mother or one of her male ancestors. Differences such as 
these must arise from strictly internal causes, which seem to set 
a natural and inevitable limit to what may be accomplished 
through selection. Here would seem to be an irreducible mini- 
mum in variation, arising directly through reduction.^ 

Control. In so far as variations arise through changes in 
hereditary matter during the pnjcesses of maturation and reduc- 
tion, they are, and must doubtless always remain, entirely 
beyond the influence of the breeder. It is quite evident that 
here is a degree of deviation and an element in breeding that 
must be left to nature antl subject to the laws of chance within 
the range of characters natural to the race. That this will always 
be a bar to absolute success is evident, but that it constitutes 
the strongest known ai'gument for purity of blood is, in the 
opinion of the writer, beyond question, because the chances of 
tmfortujmte deviations are reduced in proportion to the purity of 
blood and the absence of undesirable characters. 

Variation in parthenogenetic reproduction.'^ Had Weismann's 
original assumption been correct to the effect that se.xual imion 
is the only constitutional cause of variation, then individuals 
arising from parthenogenetic reproduction should, barring the 
influence of surrounding conditions, be alike, because only the 

1 Endeavoring to determine the function of the cytoplasm and nucleus, Boveri 
removed the nuclei from the eggs of sea urchins and afterward admitted sperma- 
tozoa to these enucleated ova. Development followed in a few cases, but the 
nuclei were smaller than in larvas normally fertilized, contained /'/// lialf tlie iiiiiii- 
ber of cJiromosoines, and the resulting larvai possessed the "pure parental characters." 

It is not supposable that anything like this occurs in nature, and yet it raises 
the cjuestion whether, after reduction, every reiiiaiiiing elenient of tlie inicleiis of 
botli parents always plays its part in development. Should it fail to do so for any 
reason, herein would lie a sufficient cause for the occasional remarkable resem- 
blance of offspring to one and not the other parent. 

2 While in all higher animals and plants a union of a male with the female cells 
is necessary to each fertilization and to the production of young, it is by no means 
true among other organisms, especially in rotifers, crustaceans, and insects with 
which "parthenogenesis lias become a fi.xed physiological habit," through which 
the unfertilized female cell develops a perfect individual. 

It is now well known that the queen of the honeybee, if prevented from mat- 
ing, will yet lay eggs capable of development, but they will all be drones (males). 
After mating she can lay either fertilized or unfertilized eggs, the fertilized devel- 
oping into workers (undeveloped females), — or, if jiroperly fed, into Cjueens, — 
the unfertilized into drones as before. After the male element is exhausted (she 



I 78 CAUSES OF VARIATION 

female and her germ cell are involved. But individuals thus 
arising through unisexual reproduction vary zvide/y, a fact easily 
credited when the phenomena of reduction are remembered. 

Parthenogenesis being limited to lower animals, the range and 
character of variations are for the most part difficult of detection 
and measurement. It is known, however, that great differences 
in size occur among individuals parthenogenetically produced, 
and characters generally are so variable in such individuals 
as to lead to the statement that the variability of offspring 

never mates but once) she is, of course, capable of laying only unfertilized or " drone 
eggs." In this way, in crossing, the drones and the workers may actually be of 
different breeds. 

Plant lice reproduce parthenogenetically during the summer season, producing 
only females ; but as the temperature lowers with approaching autumn a mixed 
brood of both males and females appears, which, upon mating, produces the long- 
lived, winter-enduring eggs. It is noteworthy that the parthenogenetic eggs of 
bees develop males only, while those of plant lice develop females during the 
summer, both sexes appearing as autumn approaches. 

It is also noteworthy that under the artificial heat of greenhouses, approximat- 
ing perpetual summer conditions, parthenogenesis continues indefinitely, and males 
are not produced unless the plants become badly dried up. 

Parthenogenesis differs greatly in degree. It is supposed to be complete in 
certain minute crustaceans and in many rotifers among which " no males have ever 
been found." It is "seasonal" in the aphis (plant lice), and "partial" in the 
honeybee and " in some of the lower animals which are not themselves normally 
parthenogenetic, but have relatives which are." Occasional parthenogenesis has 
been frequently observed. An example is the silk moth, in which Nussbaum 
found that out of 1102 unfertilized eggs ... 22 developed . . . up to a certain 
point. It is supposed that in all cases of parthenogenesis many eggs fail to develop. 

In this connection it is noteworthy and extremely suggestive that among higher 
animals — frogs, hens, and even mammals — the unfertilized ovum occasionally 
begins segmentation, never proceeding far, however, on its parthenogenetic course. 

The student should understand that in all probability a large number of eggs 
fail to develop into complete individuals even in the most successful parthen- 
ogenesis, just as do many fertilized ova fail along the way (see Weismann, Essays 
on Heredity, I, 175). There are all degrees of parthenogenesis, from the perfectly 
successful down to zero. 

Bearing upon the general subject are the interesting e.xperiments of Loeb in 
artificial parthenogenesis, especially of the sea urchin, normally bisexual, but which, 
after immersion in a saline solution of high density and subsequent return to nor- 
mal sea water, commenced segmentation and afterward developed living larvas. 
Magnesium and potassium salts proved most effective, though in general any 
treatment avails that serves to withdraw a portion of the water from the unfertilized 
egg (see Loeb in American Journal of Physiology, III, 434; also Loeb, Studies 
in General Physiology, Part II, pp. 576-626, 638-692 ; Methods, pp. 766-772 ; 
Geddes and Thomson, Evolution of Sex, pp. 1S3-198). 



INTERNAL CAUSES OF VARIATION 179 

asexually reproduced is not "immensely reduced below the vari- 
ability of the race." ^ 

In the honeybee only the male sex is produced parthenoge- 
netically. In plant lice it is commonly the female alone under 
high temperature, and both sexes under lower. Weismann bred 
separately two varieties of Cypris rcptans for some seven years, 
covering more than forty generations and " many thousand indi- 
viduals." One variety. A, was light in color ; the other, B, was 
dark. No males were ever discovered in either, and it is sup- 
posed that this species produces only parthenogenetically. While, 
for the most part, the descendants of each were extremely alike, 
yet " minute differences invariably existed." 

Not only was this true, but in 1887, three years after the 
experiment commenced, " some individuals of the dark green 
variety, B, appeared in the aquarium with the light variety." 
The same variation appeared a second and a third time, and in 
the last instance intermediate forms could be made out. In 
1 89 1 another case occurred, and in the same year its converse 
appeared, — a few typical light individuals among the dark 
colony that had "bred true many years." ^ Does this experi- 
ment also throw light on the origin of varieties, and were these 
mutations ? However this may be, it clearly shows that vari- 
ability is not entirely dependent upon sexual union, and that 
even distinct varieties may arise without the intervention of sex. 

The first significant fact in maturation of parthenogenetic 
eggs is that they produce but one polar body.^ 

From this point on two alternatives seem possible. In the 
first place, a second polar body appears to be forming in the 
usual manner and the separation of the nuclear matter takes 
place, but instead of passing out of the o.^^ it remains beJiind^ 
fusing again zvitJi tJie nucleus of the egg proper, which straight- 
way undergoes development, with its chromosomes increased to 

1 Pearson, Grammar of Science, pp. 472-473. 

2 Weismann, Essays on Heredity, I, 1 61-164. 

^ Often this polar body divides, giving the appearance of two, but a second one 
is not formed. It is quite remarkable, though entirely consistent, in the case of 
aphis, honeybees, and certain other forms that produce both se.xually and asexu- 
ally, that ihe fertilized eggs produce (too polar bodies but the purt/teiiogeiiefic eggs 
only one. 



l8o CAUSES OF VARIATION 

the proper number. In this case the second polar body appears 
in the role of a male element, so we may speak of this as a kind 
of '■'■ fertili:::ation by the second polar body." 

In the other form of parthenogenesis, however, there is little 
suggestion of a second polar body ; certainly no formal separa- 
tion and later fusing of nuclear matter takes place. On the con- 
trary, development takes place directly upon the extrusion of 
the first polar body, and it is significant that individuals a^'ising 
in this zvay possess but half the number of chromosomes as com- 
pared with those arising by sexual reproduction or by the method 
just described. Some species (as in Artemia) ^ reproduce par- 
thenogenetically by botJi methods, giving rise to two distinct 
varieties, one with half the number of chromosomes character- 
istic of the other. ^ 

Mutation as related to reduction and fertilization. Mutants 
seem to be departures characterized by a sudden loss of some 
racial character or by its possession in some unusual degree. 
They do not appear to be endowed with characters new to the 
race, except when artificially produced by hybridization. 

If the process of reduction means the loss of hereditary 
material, and if fertilization means its restoration, and if either 
means in any sense new combinations, then we can see in the 
two phenomena taken together, or even singly, abundant oppor- 
tunity for the most profound variations ; indeed, admitting their 
possibility through these causes, the wonder is that they are not 
yet more common and infinitely more remarkable. 

If there is in any sense, however slight, a qualitative loss 
through reduction, then by the law of chance the time is certain 
to come when something unusual will appear. Is it not more 
than likely that here lies a fruitful source of sweeping changes, 
as well as of the more obscure differences that are everywhere 
about us ? And is it not likely that still greater and more fre- 
quent changes would present themselves were it not that fertili- 
zation is for the most part restricted to comparatively narrow 
lines .'' 

1 W^ilson, The Cell, pp. 2S2-283. 

2 Artemia thus varies from 84 to 168, according to the particular method 
observed. 



INTERNAL CAUSES OF VARIATION i8l 

SECTION IV — BUD VARIATION ^ 

Variation is not necessarily connected with reproduction in 
the ordinary sense of the term. One Hmb of a peach may pro- 
duce nectarines. A single branch of a tree may assume the 
weeping habit or the cut-leaved form. Not only are these wide 
deviations between buds of the same tree well established, but 
also all shades of differences exist, showing that one part of a 
plant may vary independently of another, quite after the manner 
of meristic variation among animals. 

Bailey 2 calls attention to the fact that the plant is not 
an individual with a simple anatomy like an animal, but that 
"its parts are virtually independent in respect to (i) propaga- 
tion, ... (2) struggle for existence among themselves, (3) varia- 
tion, (4) transmission of their characters by means of either 
seeds or buds." 

Each bud, therefore, has a kind of individuality of its own. 
All but the first are developed asexually, yet all shades of differ- 
ences will be found among these different members of what we 
call a plant or tree ; hence each branch or phyton is a bud 
variety, and one which can be propagated by cuttings or by seeds 
or by both, and in either case can doubtless be improved by 
selection.^ 

Bailey makes the statement "* that "the seeds of bud varieties 
are quite as likely to reproduce the variety as the seeds of seed 
varieties are to reproduce their parents." ^ He quotes Darwin 
in saying that " moss roses (which are bud varieties) generally 
reproduce themselves by seed, and the mossy character has been 
transferred by crossing from one species to another." If this 
be true, — if bud variations are transmitted by the seed, even 
to the slightest degree, — then the changes wrought in bud vari- 
ation must be profound, extending as they do to the constitution 
of the germ, a fact which argues much for the ever-present 

1 Bailey, Survival of the Unlike, pp. 80-106. 
- Ibid. p. 105. 
•^ Ibid. pp. 90-92. 
* Ibid. p. 94. 

^ Professor Bailey does not intend to say that seeds of bud varieties are certain 
to come true, but rather that no seed exactly reproduces the parent plant. 



182 



CAUSES OF VARIATION 



liability to internal change and not at all, as is erroneously sup- 
posed, for the inheritance of acquired characters, because the 
characters in question were not "acquired" in the ordinary 
acceptance of the term, — they were the result of internal, not 
external, impulses. 

SECTION V — INFLUENCE OF THE CONDITION OF THE 
GERM UPON DEVELOPMENT 

Staleness. Both the male and the female germ cells are 
capable of living for a considerable time after maturation, so 
that fertilization may be somewhat delayed ; how long is not 
known, and what the effect of delay may be is not fully 
understood. 

Experiments by Vernon upon the ova and spermatozoa of the 
sea urchin of different ages, from nine to forty-five hours, indicate 
that the size of the larva is in some degree dependent upon the 
freshness of the germ at fertilization.^ The results of a number 
of trials were as follows : 

1. With stale ova and stale sperm the resulting larvae differed 
but slightly from the normal (in which both were fresh). 

2. With fresh ova and stale sperm the larvoe were distinctly 
larger (5.8 per cent). 

3. With stale ova and fresh sperm the larvae were distinctly 
smaller than when both were fresh (4.9 per cent). 

It is certain that the above combinations as to staleness are 
possible in the fertilization of mammals by mating and of plants 
by pollination. Whether the results are the same and whether 
the differences persist through life are, of course, unknown. The 
facts recorded are suggestive, but whether they will ever be 
useful remains to be determined. 

Individuality of the germ. That successive germ cells from 
the same individual may be substantially different, even aside 
from considerations of maturation, is a fact beyond question. 
The ear of corn, like its tassel, matures from the base upward. 
The tip kernels are not only younger but decidedly smaller than 
their half-sisters at the base. The different peas in a pod are 

^ Vernon, Variation in Animals and Plants, pp. 105-108. 



INTERNAL CAUSES OF VARIATION 183 

not equally developed. One of the twin pair of oats is more or 
less undeveloped. Is this difference in size due to season, food 
supply, room, or to some peculiarity in the germ .? It may be lack 
of room in pod-bearing plants, but it cannot be that in the case 
of corn. The strong presumption is, in the opinion of the writer, 
that these differences in size are partly due to differences in food 
supply but more largely to inherent differences in the germs. 

SECTION VI— XENIA, OR FERTILIZATION OF THE 
ENDOSPERM, — DOUBLE FERTILIZATION 

If one kind of corn be fertilized by another, the mixture will 
show the first year. For example, if white and yellow corn be 
planted side by side, the white ears will have many yellow grains, 
showing at once the effects of cross fertilization. These " off" 
kernels are the mixed seeds, but, reasoning from analogy, we 
should not expect the mixture to appear until the grains are 
planted and the generation of mixed breeding is at hand. The 
visible part of the kernel is not the germ ; it is the " endo- 
sperm," or surrounding portion, which serves as food for the 
sprout until the young plant has established itself. It is related 
to the germ much as the white of ^gg and its shell are related 
to the yolk. Fertilization is of the germ. How, then, do these 
outside parts become affected } 

It will be remembered that in the animal the female germ 
gives rise to one mature functional cell, the ovum, and three 
non-functional, the polar bodies ; that the male cell gives rise 
also to four mature cells, the spermatozoa, all functional, and 
that the nucleus of the one unites directly with that of the 
other witJwiit intervening nuclear divisions. 

In plants, however, it is found to be substantially different. 
The mature female cell, corresponding to the ovum, instead of 
awaiting fertilization, continues its activity, undergoing gener- 
ally two (sometimes more) divisions of the nucleus, giving rise 
to eight, or some other corresponding number of " sub-nuclei," 
which remain floating within the cytoplasm. It will be remem- 
bered that of these eight sub-nuclei only one is capable of func- 
tioning as an Q.gg nucleus ; also that two others remain near 



1 84 CAUSES OF VARIATION 

the center of the embryo sac to form the endosperm. It will 
be remembered, also, that the pollen nucleus undergoes a second 
division during its progress down the pollen tube and before 
uniting with the Qgg nucleus. 

Of this divided nucleus one portion unites with the single 
functional member of the female group, making the germ, and 
in cases such as are now under consideration the other joins 
with the minor members concerned with the development of 
the endosperm. In this way, by means of this kind of double 
fertilization, the endosperm is itself affected and the crossing is 
evident the first year. 

Of course this visible effect upon the endosperm is of itself 
purely transitory, having no influence upon the line of descent. 
The real effect of pollination is manifestly, as in all other ferti- 
lization, confined to the germ. 

Whether the two fertilizations are similar as to comparative 
influence of the two parents no one knows, nor does it greatly 
matter. The effect upon the endosperm enables us to detect 
the cross, if it is capable of detection, and to remove the con- 
taminated seeds if we desire to retain purity. If the object be 
to secure crossing, we shall of course subsequently deal with 
the products of the cross-bred germ, which only are significant 
from the breeder's standpoint. 

Just what species indulge in this double fertilization is not 
well known. It is, however, well established in a large number, 
and the process is supposed to be common rather than unusual. 

Effect of crossing upon fruit in general. What the layman calls 
fruit is commonly not the endosperm that has been under dis- 
cussion but the thickened and much developed fleshy receptacle 
on which the seeds are borne. It has been claimed that these 
parts are directly influenced the first year by crossing, so that the 
character of strawberries, apples, pears, melons, squashes, etc., 
depends much upon the source of the pollen used in fertilization. 

This claim has never been well substantiated by direct experi- 
ment. Dr. Burrill, of the University of Illinois, tells me that he 
crossed Crescent strawberries both with the Sharpless and with 
a wild berry especially selected for its insignificant, worthless 
fruit. Nobody was able to detect the difference in the resulting 



INTERNAL CAUSES OF VARIATION 185 

crops. So far as is known to the writer, the same principle holds 
in other fruits. It is the endosperm and not the receptacle that 
is directly affected by fertilization, and any influence upon the 
latter must be indirect and comparatively slight. 

Possible indirect effect of pollination upon the development of 
fruit. Though the receptacle is not itself fertilized, its develop- 
ment is conditioned upon that of its superincumbent seeds, 
which are themselves directly dependent upon fertilization for 
their development. 

This fleshy growth of the receptacle is, therefore, the result 
of a kind of stimulus from the growing germ, and it is con- 
ceivable that this stimulus may differ somewhat in degree, 
depending upon the source of the pollen. In this way the size 
of the fruit might be indirectly influenced by the pollen ; and 
in fruits like the pear, which are not concentric about the seeds, 
even the shape might be influenced in the manner noted. 

All this is quite independent of certain markings of fruit 
which may arise by those dispositions of color which are every- 
where responsible for stripes and spots, and whose causes are 
not as yet understood. 

SECTION VII— TELEGONY 

The term " telegony " is synonymous with "infection of the 
germ" and the "influence of previous impregnation." 

By this is meant the supposed influence of the male upon the 
female in such a way as to affect future offspring by other sires. 

Breeders of animals quite generally believe that the influence 
of one impregnation, especiafly the first, is permanent and wifl 
affect all future offspring ; indeed, some go so far as to say 
that a female once mated to a male of a different breed is ever 
afterwards, for breeding purposes, herself a cross-bred animal} 

This supposedly permanent effect of the male upon the female 
has been especially claimed for horses, dogs, and men. 

Telegony in horses. The classic example among horses, and 
the one that is everywhere cited as proof of the theory, is the 

1 This theory seems to be limited to animals. The writer is not aware that it 
has ever been claimed for plants. 



1 86 CAUSES OF VARIATION 

instance of Lord Morton's mare mentioned by Darwin.^ This 
mare bore a colt by a quagga, which was of course striped after 
the manner of his sire. She afterwards bore two colts by a 
stallion, both of which were said to have been marked with 
bars on shoulders and legs supposedly showing the effects of 
the quagga upon the offspring of the stallion. 

Professor Ewart, of Edinburgh, has recently repeated this 
experiment on an extended scale, with results showing no trace 
of the quagga beyond his own offspring.^ Recent investigations 
in contemporary literature throw grave doubt upon the essential 
accuracy of the data at Darwin's hand. They seem to show 
that the supposed resemblance of the stallion colts to the quagga 
was exceedingly fanciful, probably being nothing beyond what 
appears frequently in young horses of the purest parentage, 
dun-colored horses as a rule showing more or less tendency to 
stripes and bars. 

It is one of the best evidences of the power of tradition that 
this single instance, happening more than a hundred years ago, 
has done duty ever since to prove (.?) an exceedingly doubtful 
theory and an almost unaccountable belief. It is remarkable 
that so uncertain a circumstance, and one so easy of repetition, 
with universal experience tending constantly to throw light upon 
the subject, should have been so excessively overworked. It 
shows, as no other instance has ever shown, the persistence of 
tradition, the extent of credulity in the presence of the phenom- 
enal, and the willingness of men to repeat an assertion, or even 
an opinion, until by mere repetition it comes to have all the 
force of authority. The thanks of the world are due to Professor 
Ewart for his excellent work in disposing, by direct experiment, 
of a citation that has done damage long enough. It is to be 
hoped that the question may at least be held open until some 
sort of positive evidence is brought forward that is worthy the 
credence of careful students. 

Telegony in dogs. Dog fanciers are pretty generally credited 
with believing in telegony, especially in case of first matings. 

^ See Darwin, Animals and Plants under Domestication, chap, xiii, p. 17, of 
second edition by Appleton. (Quoted from PJiilosophical Transactions, 1821, 
p. 25). " Breeders^ Gazette, XLI, 1009. 



INTERNAL CAUSES OF VARIATION 187 

The best students, however, insist that very little real evidence 
has been produced on the subject, and none at all tending to 
prove the existence of this influence.^ 

With a view to testing somewhat the real extent of this be- 
lief, the author addressed letters to the best-known dog fan- 
ciers of the United States. Of thirty-seven answers received, 
one writer is a believer in telegony ; six somewhat mildly 
express uncertainty ; two are non-committal ; and twenty-eight 
are outspoken against the theory. The most outspoken of them 
all is a well-known fancier of long experience. Judging from 
this small number, it would seem that this belief among dog 
fanciers has been overrated. 

Proof by the method of instance. Without a reasonable doubt 
belief in telegonic influence rests upon stray instances, difficult 
of understanding by those who happened to be the observers, 
and hastily accepted as evidence. Now nobody should be more 
careful than the breeder to judge accurately the nature and 
value of evidence. A single instance may be good negative 
testimony, but it is seldom worth much as positive evidence. 
The products of breeding are so many and so various, and the 
causes of variation are so numerous and so complicated, that a 
particular result can seldom be assigned to the operation of any 
single cause. It is more likely the mixed or composite result 
of many influences, both internal and external ; and in order to 
know the effect of a single cause it is necessary to isolate the 
case if possible, or, if not, to resort to the examination of large 
numbers of cases, subject to varying degrees of influence, and 
thus indirectly to estimate the effect of any special cause of vari- 
ation. For example, stripes and bars were once common color 
markings of horses, as they are now of asses, especially zebras 
and quaggas. Consequently a certain proportion of colts, what- 
ever the parentage, will be born with traces of shoulder and leg 
markings. Now, under the laws of chance, a certain portion of 
these will be the direct offspring of striped or barred sires, and 
will attract no attention, the markings being considered heredi- 
tary. By the same law of chance a certain (smaller) portion will 
be the offspring of parents not barred, and a still smaller number 

1 Proceedings of the Royal Society, LX, 273. 



l88 CAUSES OF VARIATION 

will be the progeny of unbarred sires and out of dams once mated 
with baiird sires for other offspring. This smallest portion, get- 
ting its bars not by direct descent but by reversion, will most 
likely be erroneously considered to have derived them from the 
barred male not their sire. The same is true of other markings, 
and on such evidence as this the theory of telegony has been 
built up, and, so far as proof goes, it rests on no better founda- 
tion as yet. In order to secure evidence amounting to proof, it 
is necessary to examine large nnmbers involving both positive and 
negative evidence, in order to secure trustworthy averages. When- 
ever this has been done the theory of telegony fails of support. 

Telegony in man. The statistical method has been applied by 
Pearson^ in the case of man. He, together with Galton, pos- 
sesses data covering hundreds of individuals in English families. 
He reasoned that if the sire exerts a permanent influence upon 
the dam, tending to assert itself in all future offspring, then this 
influence must be in a sense cumulative, so that the younger sons 
in the family will tend to resemble the father slightly more than 
will the older sons, conceived before such influences have become 
established. 

His study covered 385 brother brothers and 450 sister sisters, 
taken two and two. In some instances there was considerable 
difference in ages, and in others they were successive children. 
His data covered both height and arm length, and after making 
the usual allowances for sex and age Pearson concludes that, so 
far as these characters are concerned, " n(j steady telegonic 
influence exists." 

Again, the many successive marriages of both colored and 
white women to men of opposite color should afford numerous 
examples of telegony were it a consequential force in heredity. 

Scientific objections to the theory of telegony. If telegony 
exists, its influence over hereditary characters must be explained, 
so far as present knowledge goes, in one of three ways : (i) some 
effect upon the tissues of the female such as will influence 
future ova in their maturation or the embyro in its development ; 
(2) something like a partial fertilization of immature and unde- 
veloped ova, in such a way as to influence their character at 

^ Proceedings of the Royal Society, LX, 273. 



INTERNAL CAUSES OF VARIATION 189 

maturation ; (3) the retention of the spermatozoa from the 
first mating, and their action in successive fertiHzations. 

As to the first, there is no scientific ground for assuming the 
sHghtest effect of the spermatozoa upon the tissues of the 
female. It is the ovum that is fertihzed, not the female, as was 
at one time supposed when fertilization was regarded solely as 
a stimulus. 

As to the second, there is no ground for believing that the 
nuclei of growing immature oogonia are in condition to unite, or 
that they are capable of uniting, with the nuclei of other cells in 
any capacity whatever. 

As to the third, there is every ground for believing that the 
spermatozoa are not retained for any considerable time, else 
successive births would occur from a single mating. Moreover, 
as but one spermatozoon takes part in fertilization, the blended 
effect of two sires is impossible. It is even impossible in multiple 
births when two services are close together. If a litter of pigs 
is the result of two matings by different sires, some may resemble 
one sire and some the other, but none will resemble both. 

SECTION VIII — INTRA-UTERINE INFLUENCES 

It is a widespread tradition that distinct characters, especially 
abnormalities, may be impressed upon the individual while /// 7itcro 
through the imagination or other strong mental impression of the 
mother. It has even been held in the case of hens, which would 
necessitate the exertion of the influence upon the ovum itself. 

The usual argument is that thg intimate contact between 
the mother and the fetus renders the latter peculiarly susceptible 
to influences affecting the former. Thus marks and deformities 
of all sorts are popularly attributed to unfortunate sights and 
experiences of the mother before the birth of the young. Pecul- 
iarly marked calves are said to owe their markings to the strong 
mental impressions created by a steer or by other cows, and colts 
are believed by many to owe their color not so much to the sire 
as to the gelding mate that worked beside the dam while she was 
carrying her young. Persons with whom the tradition is strong 
often display a blanket of a pleasing color before the eyes of the 



I90 CAUSES OF VARIATION 

mare at the time of service, and of course are extremely care- 
ful to protect her from unpleasant colors of any sort.^ The 
hold of this theory upon the popular mind is the best example 
afforded by breeding of the strength of tradition. The supposed 
reason on which it rests has slight basis in fact. The contact 
between the mother and the fetus is not so intimate as is popu- 
larly supposed. The fetus is absolutely dependent upon the 
mother for nourishment, it is true, and it lies floating in its 
fleshy incasement, which is in intimate contact with the tissues 
of the uterus ; but there is no organic connection, no nervous 
interrelation whatever. 

Anything which would curtail or shut off nourishment would 
of course injure or destroy the fetus. It is also subject to other 
accidents, as becoming entangled in its own cord, which may 
thus divide a limb or cause strangulation, — all of which, how- 
ever, is quite aside from the matter in point. 

The real question is whether, and to what extent, the fetus is 
influenced by peculiarities of nourishment during its develop- 
ment. It would of course be injured by poisons, and the danger 
from administering anaesthetics is great, but this discussion is 
limited to the direct effect of mental impressions. 

The indifference of the fetus to its source of nourishment is 
shown by an experiment of Heape,^ performed for another pur- 
pose, but throwing light upon these questions. In this experiment 
" two segmenting ova were obtained from an Angora doe rabbit 
which had been fertilized by an Angora buck thirty-two hours 
previously, and were immediately transferred to the upper end 
of the Fallopian tube of a .Belgian hare rabbit which had been 
fertilized three hours before by a buck of the same breed as 
herself. In due course this Belgian hare doe gave birth to six 
young. Four of these resembled herself and her mate, but the 
other two were undoubted Angoras.'*^ . . . Both of the Angoras 
were born bigger and stronger than any of the other young, and 

1 For a good collection of alleged instances, see Miles, Stock Breeding, 
pp. 281-295, or consult any neighborhood oracle. 

2 Vernon, Variation in Animals and Plants, pp. 1 19-120; also Procei'dim^s of 
the Royal Society, XLVIII, 457. 

3 The Angoras were characterized and easily distinguished by their long, 
silky hair and their habit of swaying the head from side to side. 



INTERNAL CAUSES OF VARIATION 191 

they all along maintained their supremacy in this direction." 
Whatever this experiment proves or does not prove, it shows 
conclusively that a fertilized Angora germ preserves and develops 
its inherent characters perfectly in an exceedingly foreign envi- 
ronment, on which it evidently depends only for nourishment. 

Mental impressions and nervous conditions are commonly in- 
voked to explain birth marks and other natural abnormalities, such 
as the loss of a finger. In this connection two facts are to be 
carefully considered : first, there is certain to occur a large num- 
ber of marks (" strawberry," " cucumber," and others) and many 
malformations of one kind or another. Scarcely an individual is 
absolutely free from something of the kind. Again, mothers are 
subjected to all sorts of sights, sounds, and experiences during the 
many weeks of embryonic development, and it would be strange 
indeed if out of the thousands of cases some correspondence 
between marks and experience could not be figured out, espe- 
cially by one whose belief is fixed and who, having the case at 
hand, needs only to find the proper " corresponding experience." 
The law of chance alone will insure an occasional correspondence 
between the two, — entirely enough to start the tradition and 
to maintain it afterward. As in theories concerning the control 
of sex, any theory stated will be verified half the time because 
there is but one alternative, so here, while the alternatives are 
more, the correspondence is certain sometimes to appear under 
the law of chance alone. 

Another fact to be reckoned with is that if the fetus were so 
sensitive to mental impressions as to require the display of 
properly colored blankets, — if females were so susceptible as 
this to surrounding sights, — what a jumble of colors our domes- 
tic animals would speedily display. In the opinion of the writer 
this tradition has neither a scientific basis nor well-established 
instances, and it is time it no longer occupied the minds of 
breeders to the exclusion of far more important matters. In this 
connection it is worthy of remark that if the average breeder 
were half as familiar with important facts, and half as attentive 
to their bearing upon his operations, as he is familiar with and 
attentive to floating traditions, we should have a far smaller 
proportion of worthless animals. 



192 



CAUSES OF VARIATION 



SECTION IX — REVERSION AND ATAVISM 



These two terms are used to designate characters appearing 
in the offspring but not visible in the parents. " Reversion " is 
used to indicate resemblance to a comparatively near-by ancestor, 
not the parent, while "atavism" refers to exceedingly remote 
ancestors, sometimes of other and foundation species. 

Thus, if a dash of impurity of blood enters a herd, it will 
appear occasionally for many generations. This would be 
spoken of as a " reversion to the strange blood." If a sire or 
dam has some peculiar character, like white stockings in horses, 
a peculiar horn in cattle, or a habit in man, it is likely to appear 
from time to time in future generations, even after its real 
origin is forgotten. This is a reversion. English breeds of cattle 
are developed from the ancient wild white cattle of Britain, and 
the occasional appearance in all these breeds of a white calf 
with red or brown ears, lower legs, and tail brush is to be 
expected. It is a reversion, not a proof of mixed blood. Of 
course the animal so marked is useless for breeding purposes, 
but no reproach to the herd, and none necessarily to the dam that 
produced it, for reversions for the most part seem to come singly. 

Atavism, on the other hand, goes farther back. For example, 
mammals during their early embryonic development still show 
traces of the gill slits, thus betraying their undoubted one-time 
connection with the same stock which gave rise to the aquatic 
animals. These gill slits occasionally persist, failing to close, 
and give rise to the abnormality known as "cervical fistula." It 
is an undoubted atavistic abnormality, — an extreme case of 
course, because of its antiquity. 

Cases of this kind are to be carefully distinguished from mere 
meristic variations. For example, the sudden appearance of a 
three-toed horse would be regarded as atavistic, for all horses 
once had three toes ; but a sixth digit in man is certainly not 
atavistic, for we have no evidence that man ever possessed 
normally more than five digits. The criminal instinct in certain 
men is undoubtedly atavistic, showing not so much a delight 
in evil doing as an entire absence of the higher sense of right 
doinof. 



INTERNAL CAUSES OF VARIATION 193 

There are certain intermediate cases difficult to name. An 
occasional cow gives no more milk than her wild progenitor ; a 
hog resembles not his immediate kind, but his striped and long- 
nosed ancestor, the wild boar of the bush ; the horse or the 
sheep paws snow the first time he sees it, though cattle do not ; 
the dog turns many times around in lying down, as if making his 
nest ; the occasional horse has bars on his legs and stripes on 
his shoulders. Which term shall be applied .? 

These are undoubtedly line cases, and all would not agree as 
to whether they should be regarded as reversions or instances of 
atavism. Because of our very frequent need for a term to cover 
experiences met almost every day by the breeder, and due to 
more near-by causes, the writer is of the opinion that it is better 
for our purposes to extend the meaning of the word " atavism " 
well forward, making it cover cases of remote characters, even 
within the species (like those just given), leaving the term 
" reversion," which will be much more frequently needed, to cover 
the more near-by cases that occur every day in our herds, and 
that would be traceable, could we know all the facts, to an old 
but not remote ancestor. 

Inheritance is from the race. It is evident that inheritance is 
not limited to the visible characters of the immediate parent. 
We constantly forget that every individual is possessed of and 
capable of transmitting all the characters of the race to which 
he belongs. We forget that his visible characters are not his 
total possession, but only those which are relatively most prom- 
inent in his case. Other combinations are easily possible out of 
the same elements in slightly different proportions, and it is not 
so strange as we think that a character once in possession of a 
race tends to persist indefinitely and, perforce, occasionally to 
become visibly apparent. It is as bound to appear, under the 
law of chance, as is the one black ball in the box of a thousand 
or a million, if only throws enough are made. 

The work of Galton, while mostly confined to man, yet shows 
clearly that inheritance is not in strict line with the visible 
parental characters, but is in large measure independent of the 
immediate parents.^ 

^ See the Regression Table, sect, iii, chap. xiv. 



194 CAUSES OF VARIATION 

Galton has endeavored to assess mathematically the fraction 
of direct inheritance, or, more accurately, the similarity between 
the child and its various ancestors. From his studies he con- 
cludes that the visible or dominant characters of the child are, 
on the average, inherited (that is, correspond with those of the 
various ancestors), roughly, as follows ^ : 

From the immediate parents 50 per cent 

From the grandparents 25 per cent 

From the great-grandparents 12.5 per cent 

From the great, great-grandparents . . . 6.25 per cent 
Earlier ancestors in proportion 

Pearson, working with larger numbers and diverse characters, 
concludes that Galton's fraction of direct inheritance (0.50) is 
too high, and is inclined to believe it not above 0.40 for blended 
characters. The subject will be pursued farther under " The 
Law of Ancestral Heredity," but this glimpse into the nature of 
inheritance is the best method known to the author to dissolve 
the almost supernatural mystery that has been thrown around 
reversion and its natural corollary, latent characters. The study 
can be pursued no farther at this point, but what has been said 
will serve to show that reversion (regression) is a fertile cause 
of variation as calculated from the type of the parent. It will 
serve also as an introduction, preparing the student for the more 
serious study of inheritance later on, when we shall learn that 
the real type, from which all departures should be reckoned, is 
the type of tJie race, and not the special type of the parent, or 
even of the mid-parent. 

SECTION X — INDIVIDUAL CHARACTERS DEPENDENT 

UPON SEX 

That both sexes possess and transmit all the characters of the 
race is a well-established fact in evolution. It is also true that 
the particular characters to undergo development, and the extent 

1 Vernon, Variation in Animals and Plants, p. 123; Proceedings of the Royal 
Society, LXI, 401, 1897; Galton, Natural Inheritance, p. 191. This does not 
mean that every individual will inherit in this proportion, but that the fractions 
express averages. 



INTERNAL CAUSES OF VARIATION 195 

to which they will develop depends very much upon the sex of 
the individual. How much allowance to make on account of sex 
in comparing one individual with another of a different sex we 
are in most cases unable to say, — not from the impossibility of 
knowing, but from the fact that in respect to most characters 
the matter has not yet been worked out. It is easily possible, 
however. 

For example, in respect to stature, men are 8 per cent taller 
than women, so that when the heights of the latter are multi- 
plied by 1.08^ the two are strictly comparable, and not before. 
When this is done the difference due to sex has been eliminated, 
and the statures of men and women may be directly compared. 

In general, males and females exhibit the same characters, 
but in varying degrees. For example, the woman as well as the 
man has hair on the face, but in less amount ; the male as well 
as the female has nipples, but they are rudimentary. Among 
mammals and the domestic animals generally the male is heavier 
in front, generally of a more robust build, and considerably 
larger than the female, — a distinction that by no means holds 
in animal life generally. 

In the present state of knowledge we simply know that the 
general appearance of the individual and its character devel- 
opment are largely dependent upon its sex ; but to what exact 
extent remains in most cases to be determined, and the deter- 
mination must be made before we can compare individuals of 
different sexes with any degree of accuracy. Without a doubt 
distinctions in sex have been greatly overworked, the differ- 
ences being mostly of degree rather than of kind ,2 and far less 
consequential than has been supposed. 

Individuals deprived of their sexual organs by castration or 
by spaying do not develop their primary sexual characters. The 
castrated male is not a female, as is sometimes erroneously 
believed, but a male arrested in his development ; and the spayed 
female is an undeveloped female. As would be expected, both 

^ These data are the result of Gallon's study of the stature of English people. 
See Galton, Natural Inheritance. 

2 It is idle to attempt to prove that certain characters, aside from those of 
reproduction, are especially identified with one se.v. 



196 CAUSES OF VARIATION 

take on the secondary sexual characters (those dominant in the 
other sex) prematurely young.^ 

Many entire individuals never develop strongly the primary 
characters of their own sex. There are effeminate males and 
mascuHne females, — those in which the characters of the oppo- 
site sex are unusually developed. It is needless to say that such 
individuals are not the best parents. , • 



11— INTERNAL INFLUENCES AFFECTING THE 
RACE AS A WHOLE 

Over against those causes that may operate in the case of 
each individual to warp its development are to be considered 
those that influence the race as a whole, turning the line of 
descent more or less permanently aside from former channels. 
Some of these influences are clearly defined and easily recog- 
nized ; others are problematical, the discussion not having yet 
passed beyond the stage of a plausible theory. 

The student of thremmatology and the breeder should be 
always mindful tJiat the purpose of all good breeding is not simply 
to hold what zvc already have bnt to produce nezv types better 
adapted than the old to the purposes of man. Accordingly any 
and all lines that promise any hope of success should be assidu- 
ously investigated. 

SECTION XI— RELATIVE FERTILITY, OR GENETIC 
SELECTION ■' 

The assumption that all members of a race are equally fertile 
/;/ se and inter se (of themselves and between each other in all 
directions) is not only hasty but dangerously incorrect. To 
quote Pearson, " Fertility is not equally distributed among all 
individuals." 

1 The entire animal with increasing age, its own sexual characters abating, 
begins to take on those of the other sex. Thus the hen grows spurs, the cow 
bellows and paws the dirt, women grow scanty beards, and old men's voices grow 
light. 

■^ Pearson, Grammar of Science, pp. 376, 414, 437-449, 462. 



INTERNAL CAUSES OF VARIATION 197 

If this be true, and practical breeders know that it is true, 
then an interesting and important question at once arises ; 
namely, What characters are correlated zvitJi the highest fertility ? 
This is important, because these are the ones that will become 
the dominant characters of the race, certainly unless opposed by 
the most rigid selection or by other powerful influences. This 
is genetic selection, — an ever-present influence over the line of 
descent, tending to establish what might be called a natural type. 

Unfortunately we possess no accurate data on this point 
among domestic animals, but Pearson's work ^ among men and 
plants is sufficient to settle the principle that such a definite 
influence exists. 

He finds, for example, that daughters are not taller than 
their mothers, but that they are taller than wives in general. 
Now not all wives are mothers, and these data mean simply 
that taller women are on the average more fertile. There is 
thus some correlation between fertility and stature. This is 
genetic selection, and under it the stature of women (English) 
may be expected to gradually increase until such correlation is 
satisfied, unless held back by other influences. 

Mothers are less variable, but daughters more so, than 
wives in general ; that is, progressive selection exists, for not 
all daughters marry, and not all who marry produce young. 
If the standard deviation from the race zvere the same for each, 
then no selection wonld be involved, but it is progressively less 
from daughter to wife and on to mother. TJie difference betzveen 
daughter and rvife is due to preferential mating, the especially 
ugly ijidividuals being less likely to find a mate ; but the differ- 
ence betzveen wife and fnother is due to relati'-oe fertility. 

The fact that in general the mother is nearer the average 
than is the wife shows that the race is fairly stable ; but the 
fact that wives are shorter than mothers has but one meaning, — 
that in respect to stature the race is yet unstable. 

Extensive studies in eye color indicate that dark-eyed indi- 
viduals, both men and women, are slightly more fertile than are 
the lighter-eyed. This means that the dark -eyed will progress 
(increase) upon the light-eyed and the race will grow darker-eyed, 

1 Pearson, Grammar of Science, pp. 441-445. 



198 



CAUSES OF VARIATION 



unless the tendency shall be held in check by the greater attract- 
iveness of lighter eyes, — preferential mating. This would be a 
long and slow process, but it would avail much to reduce, though 
it could never overcome, the effects of the higher fertility of the 
darker-eyed individuals. 

Pearson collected 4443 capsules of wild poppy. ^ They showed 
the following distribution arranged according to the number of 
stiermatic bands : 



Bands .... 


5 


6 


7 


8 


9 


10 


1 1 


12 


13 


14 


15 


16 


17 


iS 


19 


Frequency. . 


I 


II 


3- 


56 


148 


363 


628 


925 


954 


709 


397 


155 


51 


12 


I 



The largest number of capsules (954) had 13 bands and the 
next largest number had 12. Very few had so many as 18 or 19, 
or so few as 5,6, or 7. The type number of bands is then 13. 

He provided receptacles and kept the seeds of each group 
separate. He says : 

To my great surprise, however, my receptacles for 12 and 13 were 
filled up with the contents of very few capsules, those for i i and 14 more 
tardily, those for 10 and 15 only with emptying a great number of capsules, 
while I could hardly get any seed at all from those capsules with very many 
or very few bands ; they were practically sterile. The type capsules were 
enormously fertile, [while] those with even a moderate deviation from it 
[were] relatively or even absolutely infertile." 

This being true, the poppy has become about as stable as is 
possible, for its highest fertility is with its most numerous popu- 
lation. This plant was growing wild in nature. Obviously the 
great bulk of seeds distributed would be of the type number, 13 
or near it, and the mass of descendants would arise from seeds 
close to the type. What chance now would there be in nature 
for a large colony of six-or seven-banded strains to arise } Very 
little, unless they happened to possess some decided advantage 
in the struggle for existence, in which case the type would 
speedily shift in that direction ; but as long as the highest 
fertility remained with the higher number of bands, the race 
would be unstable. 

1 Pearson, Grammar of Science, pp. 443-444. 

2 Ibid. p. 444. 



INTERNAL CAUSES OF VARIATION 



199 



Suppose it were the purpose of man to develop a poppy with 
fewer, or with more, than the natural number of bands, — say 
seven or seventeen. Under what disadvantage he would work 
as long as the fertility remained relatively low ! and he would 
never succeed unless he separated the plantings from the more 
prolific type. This is genetic selection. 

Breeders are constantly operating against the drag of infertility 
without knowing it, and are as often wondering why better 
results do not follow, especially when only approved mating 
is practiced. Consider the mathematics involved in, say, three 
lines of descent of different degrees of prolificacy. For the 
sake of simplicity in illustration let us suppose three cows were 
living in a herd together. One of these cows raises two calves 
and becomes barren ; another raises four before she ceases to 
breed, and another six. For the sake of further simplicity let us 
suppose that one half the calves are females, and that each 
daughter descendant exactly repeats the performance of her 
dam and then becomes barren. How will the account stand in 
a few generations ? ^ 

Cumulative Effects of Fertility as shown by the Rel.ative 

Number of Female Descendants of Cows of Various 

Degrees of Fertility 





Cows 


Calves 


Generations 


I 


2 


3 


4 


5 


No. I 
No. 2 
No. 3 


2 

4 
6 


I 
2 

3 


I 

4 
9 


I 

8 

27 


I 

16 
81 


I 
243 



This tabular presentation shows that after five generations 
of this kind of breeding there would be but on^ fertile cow of 
the first order in the herd,^ while if all had been kept there 
would be 32 of the second order and 243 of the third. What an 



1 There is no longer any doubt that fertility is an inheritable character. 

2 There might be any number of living barren ones if the strain happens to be 
a favorite and is long-lived. 



200 CAUSES OF VARIATION 

opportunity for selection in the latter instance, with none what- 
ever in the former ! The first untimely death would render the 
line extinct, which is perhaps the best fate that could overtake 
a race which at best is able only to hold its initial number good. 

Of course artificial conditions have been assumed in order to 
bring out the principle. It does not work out in this regular 
and evident manner in our herds, but the principle of genetic 
selection is at work, nevertheless. It would be fortunate if it 
were more evident, for the herds are few that do not contain a 
large proportion of females that contribute nothing to the real 
line of descent, though they now and then give birth to excep- 
tional individuals. The quality is good, but the rate of repro- 
duction is too low. 

How many a breeder has spent fruitless years in ineffectual 
attempts to build up a strain excellent in itself but essentially 
infertile ! Witness the fate of that remarkable family of short- 
horns, the Duchess. This famous family, in its glory, was never 
surpassed, yet it was genetic selection that exterminated the 
line. Fortunate indeed is the breeder who knows this principle 
and realizes its full power whenever he finds himself opposed 
by it. 

The student must not get the impression that genetic selec- 
tion is an enemy only. A prolific line tends as strongly to 
establish and maintain itself as does a barren one to rush head- 
long to extinction. Genetic selection is therefore a friend pow- 
erful for good, as well as an enemy powerful for evil ; but it is 
as quiet and unobtrusive in the one relation as it is insidious 
in the other. The breeder has only to be eternally conscious of 
the fact that if he is to succeed he must have numbers, not 
occasional births, but regular and generous. Then he may be 
sure that he is not trying to do a thing on which nature has 
set the seal of her disapproval through non-production. However 
worthy and however valuable intrinsically the strain may be, it is 
worthless unless he can produce it with certainty and in any 
desired numbers. " Beware of the shy breeder, and treasure the 
old female that breeds regularly and true." This doctrine estab- 
lishes a cooperation with nature that insures results, and with- 
out it genetic selection will work against us, not for us. 



INTERNAL CAUSES OF VARIATION 20 1 

SECTION XII — PHYSIOLOGICAL SELECTION 

The term "■ physiological selection " refers to the fact that cer- 
tain individuals, fertile enough of themselves, will yet absolutely 
fail to breed with 2^ particular individual of the opposite sex.^ 

This principle is now well established and is recognized as a 
large cause of fruitless marriages. Individuals are frequently 
barren in one marriage and perfectly fertile in another. Physio- 
logical selection is a phase of genetic selection, and while of 
extreme importance in the marriage relation it constitutes no 
special menace to our herds. In general it has little bearing 
upon the development of a breed, but is often exceedingly 
troublesome when it is desired to effect a particular combination 
of blood lines. 



SECTION XIII — SELECTIVE DEATH RATE; LONGEVITY 

The total population depends as much upon longevity as upon 
fertility and the prevailing type at any moment depends as much 
upon the individuals that die out of the world as it does upon 
those that are brought into it. 

If the draft by death is equal, or rather proportional, from all 
types of the race or breed, then the existing type will be the 
same as that born into the world ; if not, it will be different. 

As there is little use in attempting to breed a strain, however 
desirable, that is not at least fairly prolific, so there is little use 
in spending time and expense upon short-lived strains, especially 
of milch cows and horses, which are valuable largely in propor- 
tion to age. 

For reproductive purposes the " age " of an animal is the age 
at which he stops breeding, but for other purposes it is the age 
at which he can no longer render valuable service in the desired 
direction, such as labor. 

1 This principle was first announced by Romanes (" Physiological Selection," 
Journal of the Liniuraii Society, XIX, 337-41 1), though what he had in mind evi- 
dently included what is now known as "genetic selection." It was proposed as 
showing that other principles are at work to fix types, aside from the struggle for 
existence. 



202 CAUSI'lS Ol' \ AKI AtlON 

VVi'isniimn ' believes lluil in naline llie deatli point has been 
lixcil at an a^e niosl piolilable to tlie lace as a whole. Tliat is 
to say, it is best lor the raie (i) ihal onl\ llie slionj^i-sl sliould 
sui\i\e to the hii-edinj;' aj;e ; (.') thai these should live as lon^ 
as theN aie able to leproduei-; and thai (•;) lhe\' should then die 
and (H'ase lo oe( up\' looni and t onsuine lood whith would other- 
wisi- be axailabU- lt>i the sustenante ol nioie robust iiulivi(hials 
cn^aj^ed ii\ lepiodui lion. This li.\es the death jtoint theoretie- 
ally at llu' ei'ssation ol n-pioduetion, e.xeept in sueh spc-iies as 
those in uhieh the \ount; neeil the eare or the eduiatixe assist- 
ance ol the niother. I n thest" the theoietieal death point would bo 
at the nialuiily ol the last xouni;. 'This ol eouise is in lelerenec 
to wild species, and Weisniann believes that natuie has estab- 
lished the death |)oinl in elose eorrespondenee to this piineiple. 

llowi'xer that ina\' be, then- is a piobleni here lor the breeder, 
it is loi him to li\ the death limit well be\'ond the pc-riod ol tin- 
particular service rcqiiircit. In natuie there is but one object in 
lite.— sell preservation and repuxhulion. (^n our farms there 
aie olhei objeils. The horse is lor labor, and his sei\iceable 
ai;e as well as his dei;ree ol intellij;eiue needs lo be lengthened 
as nuuh as possibK-. In nature early and ra|)id leprochution is 
a lull e(|Ui\aleiU lor loni;e\it\'. it is not so on oui' laiins, wheie 
the u\di\idual counts lor more, and e\en lapid leproduction 
I annot lake the plaie ol lonj; lile and laithlul service. 

Si'.CriON \1\' r.Al'ilMU" INI'Il'llNClCS 

I )o species possess inheriMit UMulencies to \ai\ .■' II a race 
could be surrounileil by positiveh unehani;ini; conditimis, if it 
louKl pioduie asexuallv. and il all types were eiiually vii^orous 
and ei|ually lertile, K'oiild it remain constant? Some variation 
would aiise lhiouj;h reduction, but this wouKl be heleroi;eneous, 
— that is, now in one tlirection, now in another. The real c|ues- 
lions the balhmic evolutionist asks aie these : Is there a tend- 
enc\ lor the t\ pe to ilrill, indepeiulenl ol selection or surroundinj;" 
inlluences ^ Are its tiexiations iharacteri/.eil by a continual bias 

' Wi'isinaiiM, l'",ss.iys on 1 K-iiHlity, 1, i i i i(>j; ,^00 also I'tMisoii, Cluiiuos of 
l>iMlh, PI). \-.\2. 



INTI'lkNAI, ('AlISi;S Ol' VARIy\ri()N 203 

in favorite dircclions ? Docs it vary progressively because 
impelled in these directions by "^Movvtli force" or other inherent 
energy? Are s])ecies iu-hi to tlu-ir |)resent standards by oiitsitle 
influencx-s ? or, if ncU " held," arc they driftinj^ in spite of us? 
Is the life principle constant or |)eriodic in its activities; and 
are those internal energies that vitalize matter and that determine 
development and differentiation, are they indifferent as to the 
trend of the type, or do they run more easily in some channels 
than in others? Is variation in some sense subje( t to and directed 
by a natural bias? This is the field of bathniic evolution,' and 
these are the (|uestions involved. No one is more interested in 
their discussion thini is the bree(K-r ol domesticated forms. 

Two principal theories covering the field of bathmic evolution 
have been ])roposed, both incaj)able of absolute proof, as all such 
theories nnist be, but both of interest to the- breeder. 

Acceleration or retardation of growth force. This print i])le is 
annouiK ed by ("o|)e- as an intcM'iial and e\er-|)resent cause ol 
progressive evolution, rumiing thiough all loinis ol lile and 
beneath all ordinary influences, impelling unnoticeably but irre- 
sistibly in certain directions. It is, after all, according to this 
author, the most subtle and most potent cause; ol departure; I rom 
type. The horse has undergone steady progressive development 
from an animal of the si/.e of a jack rabbit up to his present 
|)ro|)ort ions and perfection. This is due, a((oi(ling to ("ope, 
not so much to selection as to a continuous, peilia|)s almost 
unprecedented, araliration of ^i^iv7vth force. 

This theory attem|)ts to e.\])lain much of evolution through 
the energy of growth, thus throwing into the discussion a 
dynamic element commonly neglected by evolutionists. In this 
connection Pearson pertinently remarks: 

'I'licrc is iiotiiiiij; more (of less) mis( icMitific in iisin^ an inherent growth 
force to explain (lie .se< niar c lian^e.s in living forni.s tiiau in nsing tlie force 
oi f^ravitalion inlierent in tnatter to explain the (levclopnicnt ol jjlanetary 

' i'e.irson, ( iiaiiMiiai of Si icn(c, ])p. t,-j <:, 577. 'i'lic (cini "l)atliini< " as liere 
used does not include j;enelii: selcclion 01 any olliei sclei live aj^enl, internal or 
external, l)etaiise tlie effects of all su( li influences lend to come to a rest and 
not to constitute a "continual bias." 

'■^ (Jope, Origin of the Fittest, pp. i}i-.30, ic;o-iy2, y)(>-y)^ \ I'riniary Factors 
of Organic JCvolution, pp. .17.3 -.1'>1. 



204 



CAUSES OF VARIATION 



systems from nebulie. The ultimate action of vital units in each other's pres- 
ence would be no more, nor less, of a mystery than the ultimate action of 
material units. . . . The real objection to bathmic evolution lies not in any 
a priori reason against an inherent growth force, but to the obvious histor- 
ical fact that such a force has been used to cover all sorts of obscure reason- 
ing and even sheer foolishness. Science would welcome above all things a 
description of the action between vital units as simple as the law of gravi- 
tation, provided it gave a causal account of variation ; and the welcome 
would be none the less sincere if the action showed that variation was biased 
and that evolution would be irreversible even with a reversed sequence of 
physical environments.^ 

Cope's theory of acceleration or retardation of growth force 
is of course merely quantitative, and would explain any differences 
that might arise through either size or proportions of parts, or 
faculties dependent upon such proportions. It does not attempt 
to explain the introduction of characters, and if it can be in any 
way controlled no method has yet been pointed out. 

We all allude to the same general thought when we use the 
words " vitality " and " constitution " to denote not so much ten- 
acity of life as vigor of growth, and we all recognize that some 
individuals and some lines possess this faculty in much higher 
degree than others. Some individuals never survive the embry- 
onic stage ; others die in infancy ; still others reach full maturity, 
and a few persist to an advanced age. As death comes only with 
the failure of some vital function, the individual may persist long 
after he is stripped of everything that makes life enjoyable. 

It is so with races. Some seem endowed with phenomenal 
vigor, while others are preserved from extinction only with the 
greatest difficulty and by the narrowest margin, not only because 
of low fertility but also by reason of inherent lack of vigor. The 
existence of these internal forces is not a matter of doubt, and their 
office in directing variation is an interesting and valuable problem 
which the present state of knowledge is insufficient to solve. 

Orthogenesis. Closely akin to Cope's conception is Elmer's 
theory of orthogenesis ^ (straight creation), or, as he calls it, 
"definitely directed evolution." 

1 Pear.son, Grammar of Science, pp. 375-376. 

2 Eimer, On Orthogenesis and the Importance of Natural Selection in Species- 
Formation (pamphlets, 56 pages) [Open Court Publishing Company]. 



INTERNAL CAUSES OF VARIATION 205 

This theory of Eimer's is put forth as a protest and a counter 
proposition to the theory of Darwin, — afterward very much 
elaborated and extended by Weismann and others, — which was 
to the effect that all evolution is the result of heterogeneous 
growth trimmed down and shaped up by the extinction of indi- 
viduals possessing unfavorable characters. The natural assump- 
tion of the extreme selectionists is that utility is the basis of 
all selection, and that only useful characters will be preserved, 
the inevitable corollary of which is that all existing cJiaractcrs 
are iisefiil. 

Now the necessary consequence of selection is that after a 
time all existing forms and characters will come to " fit " or agree 
with the conditions of life, which are the natural agents of selection. 
This "fit " is so accurate as to deceive many observers and lead 
them to declare selection to be a fundamental cause of variation. 

Eimer points out two facts ^ : first, that there can be no selec- 
tion until a choice is presented, — therefore that the selective 
process follows and does not precede the origiji of a deviation ; 
that selection may and does cause the race to vary, but that it 
has nothing to do with the presentation of the variation in the 
first individual, — a position in which he is certainly correct. 

He argues, second, that it is not true that all characters are 
useful, but that many species endure those that are inconvenient 
and unfortunate, yet not sufficiently detrimental to be fatal, else 
the line would become extinct and no such instances would ever 
be seen. 

His position is that, first of all, "organisms develop in definite 
directions wdthout the least regard for utility, through purely 
physiological causes, and as the result of organic groivtliT ^ 

Then, after all the characters have developed together, they 
are passed upon by natural selection in the struggle for existence, 
this process blotting out only those sufficiently detrimental to 
unfit the individuals so afiflicted for continuing the struggle in 
competition with more favored forms. Selection does not remove 
a handicap, or relieve a race from all undesirable characters. 
It eliminates only the worst, and down to a level sufficient to 
establish a kind of "equilibrium of life." 

1 Eimer, Organic Evolution, sects, ii and iii. - Eimer, On Orthogenesis, p. 2. 



2o6 CAUSES OF VARIATION 

In this view of the case characters bad and good develop 
together. The luorst ones are ehminated, but many undesirable 
or indifferent ones are left behind as not being sufficient to turn 
the scale against the individual or the race. Thus many undesir- 
able characters linger in all races, and, what is more to the point, 
utility is not the cause of either the origin or the persistence of 
characters, but only of their obliteration tvJien sufficiently detri- 
mental to destroy the individual and therefore cut off descent in 
that particular line. 

The writer shares the opinion that this is the true limit of the 
selection process under nature, and that the presence of unfavor- 
able characters argues for their having arisen from causes quite 
independent of selection. 

In our yards and fields we control selection according to what- 
ever standards we may please to establish, but if unfavorable char- 
acters develop in nature, where selection aims directly at life, will 
they not be likely to develop also, unnoticed, under our own selec- 
tion, espscially when we do all within our power to preserve life ?^ 

The presence or absence of a principle aside from selection, 
yet responsible for the presence of characters, turns very largely 
upon the cjuestion as to whether, after all, there are well-established 
instances of characters independent of utility, and therefore of 
selection. The presence of such characters is easily shown. For 
example, what is the utility of the scrotum among mammals } 
Would it not have been better with sheep, for instance, if the 
testicles had remained within the abdominal cavity, where they 
develop, and where they would be safe, instead of descending 
into an external sack exposed to frequent injury } Undoubtedly 
it would have been better for individuals, for many have not only 
lost these organs, but their lives as well, from this unfortunate 
position ; but the number lost is not sufficient to seriously affect 
the racer' In other words, selection has aimed at this vulnerable 

1 It is noticeable that nature allows reproduction to go on unrestricted, and 
then slays by the millions. Man cannot afford this wholesale destruction of num- 
bers. He seeks to prevent undesirable births, — a kind of advance selection that 
has both its advantages and its disadvantages. 

2 This shows that what is bad for the individual is not necessarily bad for the 
race ; conversely, what is best for the race is often hard upon or even fatal to the 
individual. This is the very essence of selection. 



INTERNAL CAUSES OF VARIATION 207 

point many times, and in numerous cases with effect, but mam- 
mals as a race have been able to endure the handicap, else they 
would long since have become extinct. 

This shows that some causes other than utility are responsible 
for the appearance and continuance of racial characters ; that 
teleology 1 is not a universal principle, and that the function of 
selection is restrictive, not creative. 

Other characters not teleological may easily be mentioned : 

1. The peculiar minute markings on diatoms and on other 
inconspicuous organisms. 

2. The green color of leaves, due simply to the fact that 
chlorophyll is green. This is no more of an inherent necessity 
than that coal should be black or gold yellow. 

3. The digital number five which runs generally through 
vertebrates, which has often been modified and often left intact. 
Certainly the original number five could not have been teleolog- 
ical. It is not enough to assume that changed conditions might 
have rendered an organ detrimental which was once useful. 
There are too many obviously useless characters. 

4. The phosphorescence of pelagic animals,^ and the pearl of 
the oyster, which is due to injury. Is this beauty useful or is it 
accidental ? ^ 

5. The bright color of deep-sea fishes. Is it any more signifi- 
cant than the (accidental) color of chlorophyll-bearing leaves ? * 

6. The horns of stags, — useful (.'') in battle, but weapons as 
dangerous to the possessor as to his enemy. 

The list might be extended indefinitely. Elmer's argument is 
that characters such as these have been produced not through 
selection but in spite of it, and through the agency of organic 
growth in definite directions, which is ortJiogenesis. It would be 
difficult to be always certain that no basis of utility exists or 
ever has existed simply because it is not now evident, yet no 

1 The doctrine that development is in line with utility and that everything is 
useful is known as " teleology." 

2 Eimer, Organic Evolution, p. xiii. 

3 Eimer, Orthogenesis, p. 10. 

* In certain leaves of bright color the chlorophyll is unable to dominate the 
stronger shades of other chemical substances, and the leaf is not green but some 
other color. 



2o8 CAUSES OF VARIATION 

careful student of evolution doubts any longer that there are 
many misfits in nature. Whether they have arisen, as Eimer 
asserts, by reason of organic groivth, and whether they are evi- 
dences of definitely directed deviation^ is quite another matter. 

There is no doubt of the persistence of a character once started, 
even in the face of selection, but whether it be necessary to 
invoke the aid of an internal directive force to explain it is a 
question upon which more evidence is sorely needed. It is 
exceedingly important for the breeder to know and recognize all 
the inherent tendencies with which he must finally reckon, and 
it may be necessary to go beyond physiological units, correspond- 
ing to chemical atoms or molecules, and invoke some form of 
"growth force " corresponding to chemical energy to explain the 
mysteries of development. Any theory, however, that will even 
reasonably account for these mysteries must be, in the present 
state of knowledge, largely an assumption, and let the assump- 
tion be as simple as possible until we can defend its complexity 
by a mass of well-established facts. In the opinion of the writer 
the existence of such a principle as orthogenesis is more than 
problematical, except as it is an expression of the relations 
that naturally obtain between physiological units, whatever they 
may be. 

SECTION XV — PHYSIOLOGICAL UNITS 

The "gemmules" of Darwin, the " stirp " of Galton, the 
"idioplasm" of Nageli, the " biophors," "determinants," and 
"ids" of Weismann, and "the "physiological units" of other 
writers are all attempts to explain inheritance of definite quali- 
ties by assuming that the germ cell which passes over from 
parent to offspring at the time of procreation is composed of 
definite units of living matter, each with its specific properties, 
among which are nutrition and multiplication, which together 
constitute growth, and — considering the separate properties of 
the different units of which a given individual is composed — 
growth in definite directions. 

In support of this general theory it may be urged that the indi- 
vidual is zvhat he is very largely because of internal qualities. 
Corn and wheat grow side by side, drawing their nourishment 



INTERNAL CAUSES OF VARIATION 209 

from the same soil and the same atmosphere. The most nour- 
ishing food and the most deadly poison are produced side by 
side under identical external conditions. A man divides his 
dinner with his dog : one portion simply nourishes the dog 
and provides energy to watch sheep or perchance to kill them ; 
the other results in strength to bless the ages, or perhaps in 
crime to shock the world, — each according not to the nature 
of the food but to that of the animal that consumes it, and 
to the support of whose peculiar energies it contributes. 

This kind of difference in living organisms is traceable to the 
endowments of a single cell, — the only material that passes 
over from parent to offspring, — and, regard it as we may, we 
must see in this single bit of living matter all the potential 
qualities of tJie race, all the differences between the corn and 
the wheat, between the man and his dog. They are all there, 
represented in some material way in the constitution of the 
germ cell. There is thus a material basis to heredity. 

We must accept one horn or the other of the dilemma : 
either conceive this single cell as directly endowed with all the 
qualities of the race, defining its development, or else endow it 
with the capacity to develop in this fashion or that according 
to stimuli. But whence come the stimuli } Certainly not alto- 
gether from without, or the man and his dog would become 
alike, if consuming the same kind of food ; and to assume that 
the influences are internal is only to push the puzzle one step 
farther away and to assume possibly an immaterial in place of a 
material basis. 

The most simple and direct explanation of the phenomena of 
inheritance and definite development is to consider the germinal 
matter as consisting of units of some sort endowed with life 
and the power of growth. This assumption of the physiological 
unit is not so violent nor so different from other accepted scien- 
tific assumptions as it at first may seem. In the non-living 
world we assume the existence of the atom, whatever its ulti- 
mate constitution, as a minute, indivisible, and indestructible 
unit of matter. The association of some millions of like atoms 
makes a measurable quantity of an element like gold, silver, 
iron, chlorin, or sodium. 



2IO CAUSES OF VARIATION 

Something over eighty distinct kinds of matter are known ; 
therefore some eighty kinds of atoms are assumed, and this ex- 
hausts the possibilities so far as unlike like atoms are concerned 
(unless other atoms are subsequently discovered or created). 

But this does not exhaust the possibilities of matter, for these 
atoms combine together, forming new units (called molecules) 
with distinct properties. Thus NaCl (sodium chlorid) is differ- 
ent in every way from either the sodium or the chlorin atoms 
that have united to produce it. In this way these (eighty) 
various atoms effect all sorts of combinations, many of them 
exceedingly complex,^ each constituting a new material unit, a 
sufficiently large number of which constitutes a measurable 
quantity of a substance whose real composition could rarely be 
predicted by any of its visible properties. The following table 
of chemical formulae is presented for two purposes : (i) to show 
the exceeding complexity of ordinary materials ; (2) to show how 
certain groups of atoms (as CH2 or C02H)^ behave as units, 
effecting profound changes in the properties of their compounds. 
It is evident that the possible combinations ^ even with the few 
most common atoms, — as C, H, O, N, Fe, Na, K, P, S, — are 
practically infinite when they are able to organize themselves 
into larger units, giving rise to complex series like the table on 
the following page.''^ 

In this table the radical CO2H runs through the entire series, 
giving a kind of genetic cjuality to the compounds, while specific 
differences accompany the varying numbers of C and H atoms 
present with the radical. It is to be noted, however, that these 
C and H atoms are in definite proportion to each other, namely, 
CnHg,,^! ; that is, for every atom of C there will be one more tJian 
tivice as many atoms of H.-^-CO^^, — all of which is extremely 
suggestive as early steps in the world of organized matter. 

1 The composition of strychnine, CiiHonNoOs, and that of grape sugar, 
C12H22O11, are both exceedingly simple as compared with many known sub- 
stances. 

2 Such groups of atoms that move together are known as "radicals." They 
are in every sense units and are capable of replacing or of displacing other atoms 
in their constructions. 

3 We are told by the chemists that more than one hundred thousand separate 
compounds are now known. 



INTERNAL CAUSES OF VARIATION 



21 1 



Monobasic Acids of the Acetic Series, CnHon+iCOaH 



Acid 



Formula 



Formic . . . 

Acetic . . . 
Propylic 

Butyric . . . 

Valeric . . . 

Caproic . . 

Qinanthic . . 

Caprylic . . 
Pelargonic 
Rutic or capric 

Euodic . . . 

Laurie . . . 
Cocinic . 

Myristic . . 

Pentadecylic . 

Palmitic . . 

Margaric . . 

Stearic . . . 

Balenic . . . 

Butic . . . 
Nardic . . 
Behenic 
Lignoceric 
Hyeenic 
Cerotic . 

Melissic . . 



red ants, nettles .... 

vinegar 

oxidation of oils .... 

rancid butter 

valerian root 

rancid butter 

oxidation of castor oil . . 

rancid butter 

geranium leaves .... 

rancid butter 

oil of rue 

bayberries 

cocoanut oil 

nutmeg butter .... 
Agaricjis integer (a fungus) 
palm oil 



tallow- 



butter 



beech-wood tar 
beeswax 



H 

CHs 

C2H5 

C3H7 

C4H9 

CsHu 

CeHis 

C7H15 

CsHiY 

C9H19 

C10H21 

C11H23 

C13H07 
C14H29 
C15H31 
C16H33 

ClvHsr; 
C18H37 
C19H39 
C20H4I 
C21H43 
C23H47 
C24H49 
C26H53 

CogHsg 



•CO2H 
•CO2H 

•co2n 

• CO2H 

•COoH 
■COoH 

•C02H 
•C02H 
•C02H 
•C02H 
•C02H 
•C02H 

• C02H 
•C02H 
■C02H 
•C02H 
■C02H 
■C02H 
•C02H 
•C02H 
■C02H 
•C02H 
■C02H 
•C02H 

•COoH 
■ CO.,H 



Observe the exceeding complexity of these compounds, and 
notice that they stand in definite series with uniform differences ; 
there are no breaks in the series and no missing members until 
we reach C.^jH^g. Note too that these compounds may them- 
selves combine with others ; thus stearin, the characteristic fat 
of tallow, is CgHg (€^8113502)3, in which case 3 H from the acid 
radical and 3 (HO) from the glycerin radical have united to form 
3 (HgO), or water. 

Above everything else in this series note the wide difference 
in physical properties arising from a slight difference in chemical 



212 CAUSES OF VARIATION 

constitiition. For example, it is significant that in this series 
both the sokibihty in water and the acid strength diminish as 
the proportion of carbon increases. 

In addition to the properties of non-living units the theory of 
physiological units as the basis for specific characters in living 
matter requires one distinctive and additional quality, namely 
life, with its attendant phenomena, — the power of nutrition 
and growth. But what are nutrition and growth } Considered 
in general terms, nutrition is simply the power of one chemical 
compound (the living) to enter into the composition of another 
(the food) and break it up and readjust its elements on a basis 
like its own, leaving the residues to take care of themselves. 

This readjustment of the non-living food to the composition 
of the living plant or animal we call nutrition, and it means 
essentially an increase of the living at the expense of the non- 
living ; in other words, growth through the numerical increase 
of living units. 

There is often readjustment in the non-living world when two 
compounds are brought together, — the weaker giving way to 
the stronger affinity, — but there is no such wholesale "carry- 
ing over" of matter from one to another as in the phenomena 
we call nutrition and growth. This is a true invasion of the 
non-living by the living world, transferring matter almost indef- 
initely, unto itself, not only preserving its own identity in the 
meantime but impressing it upon the appropriated materials 
as well. 

These physiological or vital units are therefore conceived to 
be the smallest living units, like molecules in non-living matter, 
except that they are far more complex in constitution and are 
endowed with the power of self-multiplication through nutrition. 
This requires growth and division after the manner which has 
been noted in chromatin granules, except on a scale infinitely 
more minute. 

This conception of the action of living units has its similitude 
in the non-living. Crystallization is a growth, in the sense of 
increase of size, but it is not attended by transformations equal 
to those in living matter. Furthermore, crystallization is growth 
without differentiation, except as to geometric form. Either 



INTERNAL CAUSES OF VARIATION 213 

the physiological units arc capable of a cycle of differentiated 
energies, or else the race is possessed of many kinds of units, 
each inactive until its turn, then playing its role in suitable 
order. What then establishes the order of activity and calls 
out each unit at the proper time ? Herein lies the mystery, and 
while the physiological unit seems a biological fact, it after all 
does not solve the mystery of differentiation ; it only pushes the 
problem one step farther away. 

Unsatisfactory though it is to attempt to solve the mystery 
of inheritance and differentiation by means even of vital units, 
still nothing else that has yet been proposed comes nearer 
satisfying the needs of the case, and we cannot fight off the 
following convictions, namely : 

1. That there is a material basis not only of life but of racial 
characters as well, and this material passes to the individual by 
means of the germ cell. 

2. That the processes of life are essentially chemical. 

3. That if the whole truth could be known, the physiological 
units of vital activity may not be fundamentally different from 
atoms, molecules, and radicals actuated by chemical afifinity. 
Broadly speaking, there are suggestive similarities between the 
chemical behavior of living matter and that of laboratory mate- 
rial generally, and these similarities are constantly turning up, 
even where least expected. 

Whatever the truth may be as to the unit of vital activity, of 
two things we are sure : first, there is a unit of some kind, — a 
center of activity ; and second, it is a chemical material pos- 
sessed of life. Finally, to be useful, these units must be 
conceived as capable of absorbing nourishment, and of self- 
multiplication indefinitely. 

SECTION XVI — GERMINAL SELECTION 

The difficulty in seeking causes for inheritance and variation 
is that we are likely to prove too much. For example, if sufifi- 
cient plasticity is assumed to fully account for the high degree 
'of variation that often occurs, then variation is sufificiently pro- 
vided for, but this view makes a thing like inheritance a matter 



214 



CAUSES OF VARIATION 



of extreme improbability.^ On the other hand, if influences are 
discovered which are really efficient in setting bounds to varia- 
bility, then they make the transfer of characters from parent to 
offspring so absolutely certain, regular, and fixed, as to seem to 
leave little or no possibility of variation. 

This latter is the case with the hypothesis of physiological 
units. Weismann recognized its limitations and proposed the 
theory of germinal selection ^ to account for variation as well as 
inheritance. 

This theory assumes that the " biophors," or the physiological 
units by whatever name they may be called, are engaged in a 
kind of struggle among themselves within the germ, much as 
are plants and animals in the larger world outside. 

Any theory of physiological units must include their absorp- 
tion of food and their power of self-multiplication. If these 
activities proceed at a uniform rate for each unit involved, then 
no variation would result from this multiplication ; but if propor- 
tions change, or if the vitality varies, then variation would neces- 
sarily result from these causes alone. Now these activities must 
be either constant or variable. Weismann assumes that they 
are variable ; that these units of various relative numbers and 
strengths are competitors among themselves, one with another, 
for food ; and that those most energetic in food absorption and 
capable of the most rapid multiplication will not only be the 
most vigorous but they will also exist in relatively the largest 
numbers. They will therefore tend the more to impress their 
characters upon the later development of the individual. 

Under this view of the case the "balance of power" is con- 
stantly shifting, always in favor of the most vigorous and 
rapidly multiplying units. Believers in physiological units must 
either follow Weismann in this conception or else assume on 
the part of the units absolutely equal powers of nutrition and 
multiplication, for multiplication there must be if such units 
avail anything in the role of inheritance. 

1 All things considered, inheritance and not variation is the mystery. The 
wonder is, not that individuals vary, but that they follow as closely as they do 
the type of the race to which they belong. 

2 Weismann, On Germinal Selection as a Source of Definite Variation (pam- 
phlet, second edition) [Open Court Publishing Company]. 



INTERNAL CAUSES OF VARIATION 215 

Weismann reminds us that " By far the largest part of 
qualitative modifications ... rest on quantitative changes. 
A determinant," says he, " must be composed of hetero- 
geneous biophors, and on their numerical proportion reposes, 
according to our hypothesis, their specific nature. If this pro- 
portion is altered, so also is the character of the determinant ; " 
and further: "for fluctuations of nutriment and the struggle 
for nutriment, with its sequent preference of the strongest, 
must take place between the various species of biophors as 
well as between the species of determinants. But changes in 
the quantitative ratios of the biophors appear to us qualitative 
changes in the corresponding determinants." ^ And again : " By 
a selection of the kind referred to tJie germ is progressively modi- 
fied in a manner corresponding with the prod2iction of a definitely 
directed progressive variation of the part y^ In this way Weis- 
mann would "explain" Elmer's orthogenesis; but it is note- 
worthy that none of the theories yet pivposed ivill account for the 
original introduction of a new character in the race, whether 
represented and transmitted by a physiological unit or not. 
Germinal selection would provide for changes in relative pro- 
portions of characters, and even for their utter extinction, but 
not for their introduction, unless, indeed, characters may origi- 
nate by new combinations of old elements. 

One is almost forced to the conclusion that in nature loss 
or modification of characters is far more common than their 
origin and introduction. It looks as though most of the changes 
arise in this way, yet it is conceivable that an entirely new 
quality might arise through a relatively slight modification of 
the chemical or physiological make-up of the vital units. It is 
seen and recognized that in the non-living world a slight change 
in the radical is followed by a profound alteration in physical 
and chemical properties, and that this sweeping change may be 
induced by comparatively shght and even external causes. 
May not the same be true of vital radicals or units, and may 
not new characters arise more readily than we suppose, all per- 
haps out of elements fewer, and transformations simpler, than 
we have hitherto imagined .'' 

^ Weissman, On Germinal Selection (second edition), pp. 46-47. ^ Ibid. p. 35, 



2i6 CAUSES OF VARIATION 

Control of internal causes affecting the race as a whole. 

Whatever causes of this nature may be at work in our fields 
and yards, — and they are to be reckoned with, — our control 
over them is secondary and indirect. Their effects, if present, 
are at once insidious and sweeping. 

We can be mindful of the effects of genetic selection and the 
selective death rate, and provide against them, at least to a 
large degree. If growth force and orthogenesis are also forces, 
they can be assisted or held in check by selection, but they can 
never be absolutely controlled ; and if germinal selection is a fact, 
it is going on entirely independent of any control which present 
knowledge enables us to exercise except through selection. 

Summary. All that is involved in heredity is contained in a 
minute bit of living matter passed from parent to offspring, and 
whose development will constitute the new individual. The im- 
pulse to development, therefore, and its fundamental possibilities 
are forces internal to the germ and to the living organism. 

It is not difficult to see many causes of variation in the 
internal processes known to be involved in the activities of 
living protoplasm. Growth is the result of cell division, which 
seems to proceed upon plans calculated to insure qualitative 
as well as quantitative equality as between the daughter cells. 
Any deviation from the plan, however, — and deviations are 
known to occur, — must result in variation. This is especially 
true in the reduction process which is characteristic of matura- 
tion in both sexes, and which probably lies at the basis of bud 
variation and of many mutations. 

Fertilization and sexual union are processes calculated to 
effect new combinations out of the elements involved, though 
the possibilities in this direction would be rapidly reduced by 
close breeding or by any other circumstance which simplifies 
the ancestry. 

Doubtless the condition of the germ has some influence, but 
it is not well understood. The phenomenon of xenia, or double 
fertilization in certain plants, causes the seed coats to vary the 
first year in the same direction as the germ. Telegony is a 
myth, and intra-uterine influences are doubtless limited to those 
of nutrition, except in cases of disaster. 



INTERNAL CAUSES OF VARIATION 217 

Reversion and atavism are but special instances under the 
law of ancestral heredity to be discussed later, serving to show 
that inheritance is partly from ancestors back of the parent. 

Certain internal factors are of such nature as to affect the 
race as a whole. Genetic selection is based upon the fact that 
all individuals are not equally fertile, and that the type tends 
strongly to assume that of the most prolific. Bathmic influences, 
such as "growth force" and orthogenetic bias, have been 
advanced as explanations of those inherent tendencies that 
appear to characterize most species and that give an underlying 
trend to their direction in descent. 

The basis of all vital activities is conceived as being some 
kind of living unit, comparable with the atom and the molecule 
in the non-living world, whose activities constitute growth and 
differentiation, and whose reactions with outside matter and 
with each other are fruitful causes of variation. 

ADDITIONAL REFERENCES 

Bud Variation and its Bearing upon Weismannism. By L. H. 
Bailey. Science, I, 281-291. 

Bud Variation, Causes of, and Illustration. By R. M. Kellog. 
Proceedings of the Michigan Horticultural Society, 1897, pp. 121- 
134; also in Experiment Station Record, XI, 424-425. 

Bud Variation OF Concord Grape. By W. Paddock. Garden and Forest, 
No. 456, pp. 464-466 ; also in Experiment Station Record, VIII, 290. 

Color Effects in Crossing Sweet and Flint Corns. Bulletin Illi- 
nois Experiment Station, No. 21 ; also in Experiment Station Record, 
XIII, 740. 

Determinate Variation and Organic Selection. By J. M. Baldwin. 
Science, VI, 770-773. 

The Development of the Hybrids between Fundulus Hetero- 

CLITUS and MeNIDIA NOTATA, WITH ESPECIAL REFERENCE TO THE 

Behavior of the Maternal and Paternal Chromatin. By 

W. J. Moenkhaus. American Journal of Anatomy, III, 29. 
Effect of Fertilization upon Fragrance. Experiment Station 

Record, VIII, 55. 
Effect of Spaying upon the Quality of Milk. Experiment Station 

Record, XIV, 182. 
Essays on Heredity. By A. Weismann. 2 vols. 
Evolution in a Determinate Line. By Bashford Dean. Biological 

Bulletin, VII, 105-112. 



2i8 CAUSES OF VARIATION 

Evolution on Predetermined Lines. By T. D. A. Cockerell. Science, 

XIII, 311-312. 
Experimental Study of Variation. By J. C. Ewart. Report of the 

British Association for the Advancement of Science, LXXI, 666- 

680. 
Experiments in Crossing Corn and Watermelons. By F. C. Card 

and G. E. Adams. Experiment Station Record, XIII, 740. 
Experiments upon the Influence of the Sexual Cells upon the 

Somatic. By G. W. Field. Biological Bulletin, II, 346-347. 
Heterotypical Division in Maturation. By T. H. Bryce. Report 

of the British Association for the Advancement of Science, 1901, 

pp. 685-687. 
Hybridization of Corn and Watermelons. By F. C. Card. Experi- 
ment Station Record, XI, 928. 
Hybridizing Melons: Effect in Sugar Content. Experiment Station 

Record, XVI, 229. 
Hybridizing Zebra and Horse. (Experiments of Baron de Parana in 

Brazil.) Experiment Station Record, XI, 972. 
Individuality of Chromosomes. By H. Metcalf. Proceedings of the 

Nebraska Academy of Science, 1901. 
Inheritance in Parthenogenesis. By Ernest Warren. Proceedings 

of the Royal Society, LXV, 154-158. 
Organic Selection. By J. M. Baldwin (Science, IV, 724-725; V, 

634-636), E. D. Cope (Science, II, 124), and H. F. Osborn (Science, 

VI, 583-587). 

Orthogenetic Variation. By H. F. Gadow, Cambridge. Science, 

XXII, 637-640. 
Orthogenetic Variation in Certain Mexican Species of Lizards. 

By H.F. Gadow. Proceedings of the Royal Society, LXXI I, 109-126. 
Physiological Selection. By G. J. Romanes. Science, VII, 606-608. 
Premature Fertilization Injurious to Fruit. Experiment Station 

Record, XIV, 634. 
Problem of Development. By E. B. Wilson. Science, XXI, 281-293. 
Secondary Sexual Characters. (A study of the effects of castration.) 

By S. G. Shattuck and C. G. Seligmann. Proceedings of the Royal 

Society, LXXI 1 1, 49-58. 
Sexual Reproduction ; Distinction from Asexual. By Richard 

Hertwig (translated by W. C. Curtis). Science, XII, 940-946. 
Song of Birds Kept from their ov^n Species. By William E. D. 

Scott. Science, XIX, 154. 
Sterile Fruit Blossoms. By S. A. Beach. New York Station Bulletin, 

CLXIX, 331-371- 
Sterility of Cattle, Causes of. Experiment Station Record, XI, 289. 
Telegony. By J. C. Ewart. Proceedings of the Royal Society, LXV, 

243-251. 



INTERNAL CAUSES OF VARIATION 219 

Telegony (disproved). By J. C. Ewart. Popular Science Monthly, 

LVII, 126-133. 
Telegony (disproved): Account of Ewart's Experiment with 

Zebroids. By J. C. Ewart. Breeders' Gazette, XLI, 1009; also in 

Transactions of the Highland Agricultural Society, 1901, pp. 81-134 ; 

and in Experiment Station Record, XI, 1077; XIII, 275 ; and XIV, 

76. 
Telegony (disproved): E.xperiment with Guinea Pigs. By C. S. 

Minot. Report of the Briti.sh Association for the Advancement of 

Science, 1906, p. 606. 
The Chromosomes in Heredity. By W. S. Sutton (1903). Biological 

Bulletin, IV. 
The Germ Plasm. By A. Weismann. i vol. 
The Physical Basis of Heredity. By K. H. Eigenmann. Popular 

Science Monthly, LXI, 32-44. 
Theory of Heredity and Telegony. By J. C. Ewart. Nature, LX, 

330-333- 
Xenia, Example in Apple. By L. H. Bailey. Science, IV, 498-499. 
Xenia, or Double Fertilization. (Review of work of De Vries, 

Correns, and Webber.) Experiment Station Record, XII, 421, 717; 

also XIII, 620. 
Xenia in Maize. By Hugo De Vries. Experiment Station Record, XI, 

1016. 



CHAPTER IX 

EXTERNAL INFLUENCES AS CAUSES OF VARIATION 

It was long ago noted, and the most casual observer cannot 
fail to discover, that individuals of the same species vary greatly 
according to their environment, — meaning by that term all the 
external conditions of life, such as climate, food, friends, enemies, 
and all those outside influences, favorable or unfavorable, among 
which the individual finds itself born, and with which it must 
live upon the best terms possible if it would live at all. That 
these external agencies exert a direct effect upon living matter 
is beyond question, and it remains to give attention to the nature 
and extent of this influence as a partial answer to the cjucstion 
we would solve, — the dependence of organized living matter 
u{X)n the external world for the nature and range of its activities. 
Anything we may learn upon this point will be a contribution to 
the stock of knowledge out of which we shall one day determine 
all the causes of variation. 

Without a doubt the great bulk of variability is due to 
causes internal to the organism, mainly in the form of inherited 
tendencies. Pearson, after exhaustive statistical investigations, 
remarks, " The individual contains within itself, owing to a bath- 
mic law of growth, a variability which is itself quite sensible, 
being 80 or 90 per cent of the variability of the race." ^ 

Even then, however, these internal influences are dependent 
upon outside conditions for their opportunity. A born giant 
must have food in abundance, but no amount of food would 
make a giant out of a dwarf. Nor will it avail to awaken, late 
in life, forces that once might have been active. Some dwarfs 
are therefore born and others are produced by insufficient food. 

The external conditions of life affect variability in four dis- 
tinctly different ways : (i) through natural selection, influencing 

1 Pearson, Grammar of Science, p. 473. 
220 



EXTERNAL INFLUENCES AS CAUSES OF VARLVriON 22 1 

the type ; (2) by affording or withholding the opportunity for the 
proper development of the characters born into the individual and 
therefore representing internal forces ; (3) by exerting, directly 
upon the organism, a stimulating or a depressing effect upon its 
normal activities ; (4) in extreme cases by temporarily or per- 
manently modifying the character of normal functions. 

The first manifestly affects the type and the race as a whole, 
while the second, third, and fourth primarily affect the individual. 
It is with these latter that we are now concerned. 

The hasty student credits to external conditions all that tvould 
happen if these conditions zvere ivithdraxvn. This is erroneous. 
A very large part of all that happens is due primarily to internal 
causes, because different races are differently affected by the same 
conditions. The fundamental cause of variability is therefore to 
be sought in the form of inherited characters, even though these 
are dependent upon external conditions for their development, 
W'hich may themselves seem to be direct causes of variation. 

It is therefore proper enough to speak of external conditions 
of life as causes of variability, providing we know what we mean 
thereby and are careful to distinguish between their indirect 
effect, on the one hand, in affording or withholding the con- 
ditions of development in which their influence is secondary, 
and their direct influence, on the other hand, in stimulating, 
depressing, or altering the activities of the organism. 

With these distinctions in mind we may study the effects of 
outside conditions upon variability without danger of attributing 
to them what properly belongs to inherited faculties. 

SECTION I — GENERAL EFFECT OF LOCALITY UPON PLANT 
AND ANIMAL DEVELOPMENT 

It is a matter of common knowledge that the texture and 
quality of garden vegetables depend veiy much upon the con- 
ditions under which they are grown, and that the highest flavor 
of the orange, peach, pineapple, and edible fruits generally is 
found only in specimens from certain favored localities. 

Thus cantaloupes of extremely high quality developed first at 
Rockyford, Colorado, and afterward in a few other sections. 



22 2 CAUSES OF VARIATION 

American seed growers generally seem to have settled upon 
Kansas as the spot most favorable to the development of the 
highest quality in the watermelon, and it is accordingly the 
favorite seed-producing locality. Darwin tells us that " the seed 
of the Persian melon yields near Paris a fruit inferior to the 
poorest market kinds, but at Bordeaux yields delicious fruit." ^ 

European varieties of grapes failed so utterly in eastern North 
America as to necessitate the developing of varieties from the 
native vine. 

Indian corn develops local varieties with extreme readiness, 
but they seldom succeed when transferred even short distances, 
at least until time enough for acclimatization has elapsed. The 
writer sent a standard white Illinois corn, ripening in about a hun- 
dred and twenty days and capable of maximum yields (seventy-five 
bushels per acre), to be grown in Michigan, Wisconsin, Maine, and 
Mississippi.^ In Maine it failed to ripen, but at all other points 
it ripened in about a hundred days, producing small, inferior 
ears, altogether worthless as a commercial crop. That it should 
hurry through its period of growth at the north was not surpris- 
ing, but that it should do the same at the south, where it had 
even more time at its disposal than at home, is unaccountable. 

Wheat, on the other hand, is a cosmopolitan crop, and while 
varieties succeed better in some localities than in others, yet a 
new variety seldom fails, and sometimes succeeds even better 
than in the locality whence it came. However, it is altogether 
likely that no known wheat-growing region equals England in 
natural advantages for maximum yields. This is supposed to be 
due to the humid atmosphere and cloudy skies during the later 
stages of growth, in sharp contrast to the bright skies and hot 
dry air of America at this season. If this be the true partial 
explanation of the occasional phenomenal and always high yields 
in Great Britain,^ we may hope for equal results some day in the 
similar climate of Oregon. 

1 Dan\dn, Animals and Plants, II, 264. 

2 Wisconsin, 200 miles north; Michigan, 200 miles north and 100 miles east; 
Maine, 300 miles north and 900 miles east ; Mississippi, 450 miles south. 

3 The average wheat yield of the United States is between 12 and 13 bushels 
per acre, while that of Great Britain is almost exactly 30, and a maximum of 90 
bushels has been reported. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 223 

The experiments of Bonnier upon this general subject are 
classic.^ He divided dandelion, helianthus, and many other 
plants growing in the valley, and planted one half of each indi- 
vidual plant on the mountain at an elevation of 2300 to 2400 
meters, leaving the other half in the valley (how much below 
he does not say). As the division was made by a vertical cut 
through the fleshy root, the two halves must have been practi- 
cally alike. 

He found that the portions on the mountain developed plants 
much smaller than those in the valleys. The difference was 
mainly in the length of the internodes, not in their number. 
The leaves of the dandelion were less than one fifth as long 
when drawn to scale, and the flower stalks were not one tenth as 
long. The mountain plants in general developed higher colors. 

Darwin tells us that the medicinal qualities of digitalis are 
'* easily affected by culture," and that " the wood of the Amer- 
ican locust tree {Robinia) when grown in England is nearly 
worthless, as is that of the oak tree when grown at the Cape of 
Good Hope." ^ The same author quotes Sir J. E. Tennent as 
saying that "in the Botanic Gardens of Ceylon the apple tree 
' sends out numerous runners underground, which continually 
rise into small stems, and form a growth around the parent 
tree.' " ^ If this be true, its naturally slight tendency to sprout 
has in this locality developed into a pronounced habit. 

Sheep, especially the merinos, are cosmopolitan, and yet they 
succeed nowhere else as in New Zealand. On the other hand, 
according to Darwin they seem not to succeed in the West 
Indies or on the west coast of Africa, where " the wool disap- 
pears from the whole body except over the loins."'* The writer 
has seen the same thing in Brazil, except that the best-clothed 
portion of the body was the back of the neck, the same spot on 
which the vicuna bears its fur. 

The statement is frequently made that fat-tailed sheep rapidly 
lose this character when removed from their native saline pas-- 
tures, but the assertion needs confirmation, for the writer has 

^ C. Bonnier, Recherches expeiimentales sur I'adaptation des plantes au climat 
alpin. Annales des sciences naturelles, 7*= Serie, Tome XX, 1895. 

2 Darwin, Animals and Plants, II, 264. ^ Ibid. p. 266. * Ibid. I, 102. 



224 



CAUSES OF VARIATION 



seen a respectable development of fat when the sheep were kept 
under ordinary conditions. 

One of the most remarkable and seemingly best authenticated 
instances of the evil influence of locality upon character devel- 
opment is the almost uniform failure to maintain the quality of 
certain English breeds of dogs when bred in India. We are 
indebted again to Darwin ^ for the remarkable statement that in 
that country the bulldog rapidly loses his ferocity, and of all 
dogs the hounds decline most rapidly. 

Instances might be multiplied indefinitely, but two things 
must be borne in mind by the student when dealing with this 
class of facts : first, there is the greatest opportunity for error 
or exaggeration from inexact observation and report ; second, 
the plant or animal is exposed to a multitude of new conditions 
when transplanted to a new locality, only a portion of which are 
inherent in the conditions of life. Commonly the breeders or 
attendants are not familiar with the new form and do not afford 
proper conditions, as in not giving suitable food to animals or 
in failing to afford sufficient room to large-growing varieties 
of plants.^ 

After making due allowance, however, for all these considera- 
tions, the fact remains that the conditions of life evidently do 
exert a strongly modifying influence upon development. 

Locality a comprehensive term. There is little use in attempt- 
ing to determine the exact influence of each separate locality. 
The term is an exceedingly comprehensive one, including many 
things, — climate, by which we mean not only temperature, 
moisture, and light, but their comparative proportions in that 
particular spot ; season, by which we mean the succession of 
climatic conditions ; food (both as to quantity and quality), on 
which the creature absolutely depends, not only for life but also 
for growth ; habits of life, radical changes in which may be forced 
upon the animal by its habitat. 

■ This is all too complex for profitable study and discussion. 
We must separate locality into its elements and determine, if we 

1 Darwin, Animals and Plants, I, 39. 

2 It will be noted in this connection that most of the instances cited are those 
of deterioration. 



EXTERNAL INFLUENCES AS CAUSES OF VARLATION 225 

can, the particular modifying influence of each of the conditions 
of life with which animals and plants are surrounded. In this way 
we may get important information upon this most difificult and 
unsatisfactory subject. Accordingly we undertake to ascertain 
the effects due specifically to food, temperature, light, etc., — the 
elements that, taken together, constitute the conditions of life. 

SECTION II— THE INFLUENCE OF FOOD UPON 
VARIABILITY 

The best evidence goes to show that food affects develop- 
ment both quantitatively and qualitatively. It is expedient to 
consider the two separately. 

Quantitative effects of food. In general, as every stockman 
knows, full feed means increased size, provided always there 
has been no check during development. This is not only the 
experience in the yards everywhere, but the world over the 
largest animals are found on the best feeding grounds. Doubt- 
less other external influences affect size, but certainly no other 
equals the food supply, and if maximum development is expected 
food must not be withheld, especially during the early stages of 
growth. No amount of later feeding, after the individual has 
accustomed itself to a reduced supply, can make amends for 
early shortage. This is itself a deviation which easily becomes 
permanent and follows the individual through life. 

Development, however, bears no direct ratio to food con- 
sumed ; that is to say, the greater portion of all food is consumed 
in supporting the vital processes, altogether without reference 
to increase of weight or to labor performed. Under the best of 
feeding we rarely recover 10 per cent of the food consumed in 
the form of growth or increase of weight, and seldom realize as 
much as one sixth in the form of labor or other output of the 
body. The great mass of the food is either not digested at all 
or goes to support the internal activities of the body, or else is 
digested and passed out of the body without serving any useful 
purpose whatever. 

It is a significant fact that stunted animals (and plants as well) 
seldom recover from the evil effects of arrested development. 



2 26 CAUSES OF VARIATION 

and that under-development due to insufficient food is quite 
distinct from dwarfing, especially among animals, in that the 
body does not develop proportionately. In underfed calves, for 
example, the head outgrows the rest of the body, the legs are 
long, and the joints are large. 

In general, full feed means not only increased size but early 
maturity as well, which is of even greater consequence. Because 
of the large proportion of food never recovered in gain, it is 
manifest that any shortening in the period of development re- 
sults not only in improved quality but also in the saving of feed ; 
in other words, early gains are economical gains and they tend 
to higher quality. 

Effect upon fertility. The amount and character of food often 
exert profound physiological influences. For example, the fer- 
tility of the female honeybee is mainly due to food, the sterile 
workers and the fertile queens developing from the same eggs. 
If, even after the worker eggs are hatched and the larvae well 
developed, they be taken from the worker cells, put into queen 
cells, and fed "queen's food," they will develop into queens, — 
a fact often taken advantage of by the bees themselves when by 
accident all the prospective queens have been lost. Here fertility 
is largely a matter of food, although an occasional worker is 
known to produce eggs. This general difference between worker 
and queen must therefore be regarded as one of development 
dependent mainly on the food supply. 

Speaking generally, excessive food supply leads to infertility 
among both plants and animals. The former vegetate luxuri- 
ously, but they do not blossom and fruit so abundantly as under 
a full but moderate supply of plant food. 

Whether the effect in question is due to overfeeding or to 
some one or two elements in particular is not well established. 
Enough is known, however, to justify the assertion that extreme 
proportions of nitrogen produce luxuriance in stem and leaf at 
the expense of flower and fruit, but there is exceeding doubt 
whether this effect would follow a well-balanced food supply 
with plenty of phosphorus. 

Excessive feeding of animals, especially females, tends to fatty 
degeneration of the essential sexual organs, and consequently to 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 227 

sterility, and this result is hastened if the food contains unusual 
proportions of carbohydrates, especially sugar. 

Effect of feed upon variability. It is a common belief that 
plants and animals are more variable when well fed than other- 
wise. Doubtless this is true, so far at least as appearances go, 
for only under such favorable conditions are all the faculties 
that are born into the exceptional individual able to develop and 
become visible. When a race is living under mediocre conditions 
there is a dead level in development. The mediocre individuals 
have relatively the best chance, and few will rise above the con- 
dition of mediocrity. 

Whether full feed is a direct stimulant to variability or only 
brings potential differences to the surface is therefore an open 
question. The procedure indicated is, however, in either case the 
same ; namely, to provide maximum conditions if the breeder 
expects to realize the utmost from his best individuals or hopes 
ever to find variations worth preserving. 

Herein lies the fact that well-bred animals often require more 
feed than their scrub relatives. It was upon that point that they 
departed from their kind — not that they contracted to exist on 
less feed, but that they were able to handle more feed and put 
it to good use. If the purpose of the breeder were to develop 
races with a minimum maintenance ration, it could be done; but 
we keep domestic animals not for their society but for what they 
can do, — for what they can manufacture out of corn, oats, and 
hay. We improve crops, not to see upon how poor land they may 
live, but rather to increase their ability to construct valuable food 
materials from the mineral elements of the soil and the inorganic 
constituents of the atmosphere. Not minimum of consumption 
but economic consumption is therefore the virtue sought. 

Evil effects of overfeeding. The plant will seldom suffer from 
abundance of food, although it is not impossible. Excess of 
nitrogen causes rank growth of stem, but phosphorus is needed 
for seed. Something akin to a balanced ration is doubtless best 
for plant as well as animal, yet the former has more of selective 
ability than the latter. 

The animal is easily overfed, and if so the injury is likely to 
be permanent. It results (i) in disorders of the digestive tract; 



2 28 CAUSES OF VARIATION 

(2) in disorders of the excretory organs ; (3) in excessive fat ; 
(4) in sterility, especially in females, through fatty degeneration 
of the essential sexual organs. 

Qualitative effects from the nature of the food. The color 
of plants and flowers, and even of animals, is said often to be 
directly influenced by their food, but it is exceedingly difficult 
always to separate fact from tradition in this particular field, 
because the average person has an exaggerated conception of 
the influence of food upon the constitution of the organism, 
often believing that a meat diet, for example, inclines to ferocity 
and uncontrollable temper generally. Darwin ^ mentions the 
practice of feeding hemp seed to bullfinches to darken their 
color ; the fat of a certain fish to parrots, causing them to 
" become beautifully variegated with red and yellow feathers." 
He also states that the shells of mollusks are largely influenced 
by the amount of lime in the water in which they grow, and 
Beal succeeded in growing blue hydrangeas from pink stock by 
occasional aj^plication of alum water to the roots. 

That the flavor of milk and eggs is largely dependent upon 
food has long been known, as has the specific effect of certain 
foods upon the texture and flavor of meat. Mumford found at 
Illinois that the fat of pork fed upon large amounts of cotton 
seed proved, on chemical examination, to contain a proportion 
of true cotton-seed oil, showing that a portion at least of the 
food had been carried over and stored unchanged in the tissues. 

That this is the exception, or perhaps more correctly the 
lesser result, is proved by the fact that in general the identity of 
the food is lost in the nature of the organism, showing that the 
organism and not its food dominates results. The same meat 
becomes dog or man indifferently, indicating that food com- 
pounds are not as a rule carried over but rather " suffer profound 
disruption," being reduced, if not to their elements, at least to com- 
paratively simple compounds, the energy set free in the disrup- 
tion being " utilized in the subsequent work of construction." ^ 

The higher organisms are comparatively independent of their 
food so far as qualitative changes are concerned. They seem 

^ Darwin, Animals and Plants, II (second edition), 269-270. 

2 Encyclopasdia Britannica, XIX (1885), article " Physiology," 21. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 229 

able to extract the materials for their activities often from the 
most forbidding sources and under the most discouraging cir- 
cumstances. Indeed, many forms of animal activity are depend- 
ent for support not so much upon the materials of the food as 
upon its energy. This applies more especially to mature animals 
and their functional activity, but we also remember that in the 
business of body building, materials are required in large excess 
of the actual amounts retained in the body. 

Lower forms of life, however, seem often greatly dependent 
upon their culture medium. Thus many bacteria grow quite dif- 
ferently upon the potato and in agar or in beef broth, and a germ 
disease often presents in one species symptoms substantially 
different from those it presents in another. 

The animal and the plant (among the higher forms) are 
nourished upon fundamentally distinct plans. Both require 
that food be in the soluble form before it can be useful, and 
each makes use only of such available materials as it may need. 
But the animal is provided with an elaborate excretory system 
by which it frees itself of all residues, both of undigested food and 
of broken-down tissues, and also of digested food in excess of 
requirements. By this means the animal is promptly freed from 
all redundant food material. 

It is not so with the plant. It takes in food by absorption at 
its roots, and the water carries with it anything and everything 
that may happen to be dissolved. If nothing poisonous enters, 
the plant will live, but it will be loaded with residues, because it 
has no excretory system. The water passes off by evaporation 
at the leaf surface, leaving at that point large quantities of what- 
ever was dissolved in the juices of the plant. We are not sur- 
prised, therefore, that vegetation of the same species differs 
very widely in composition in different localities, especially with 
respect to mineral content, depending upon the character of the 
soil in which it was grown. This difference may be, as in the 
case just cited, quite independent of vital processes, and due to 
nothing more than accident. 

Plants, and the simpler organisms generally, are of necessity 
far more dependent upon their environment, and especially their 
food, than are the higher animals, that have to a large extent 



230 CAUSES OF VARIATION 

freed themselves from the bondage due to the accident of birth- 
place, being able to move about and therefore to establish in the 
widest sense an independent existence. 

Notwithstanding all this, and after making allowance for the 
grosser influences over lower organisms, the fact yet remains 
that, to a slight extent, and to a slight extent only, the animal 
is influenced by the character of his food. That this influence is 
larger upon the products of the body than upon the body itself 
is certain ; and upon the subtler qualities, like flavor, rather than 
the more essentially biological characters such as structure. 

SECTION III — THE EFFECT OF MOISTURE UPON 
DEVELOPMENT 

Animals as a rule are quite independent of moisture, providing 
their direct needs for water are satisfied in the way of body 
consumption in addition to that needed to reduce the effects of 
internal heat by evaporation.^ 

Plants on the other hand do not have the circulatory system of 
animals, and they depend upon water, taken in by the roots and 
evaporated by the leaves, to actually carry food to all parts of the 
structure. Their need for water is therefore far above the amounts 
necessary for actual composition. For example, it requires the 
evaporation of something like the equivalent of eight inches of 
standing water over the entire field to mature an average corn crop. 

1 It is often erroneously taught that animals consume carbonaceous foods to 
sustain the body temperature, while the truth is that all food actually utilized is 
broken down and its energy set free. This energy is disposed of in three ways : 
first, to a slight extent in effecting the recombination of the elements of the food 
into the exceedingly complex protoplasm of the body or its products; second, by 
the body or some of its parts in the form of internal or of external work ; or, third, 
it is radiated in the form of heat of low intensity. In this way the body is a factory 
that is constantly producing heat, which must be disposed of or the structure will be 
destroyed. There are but two ways of doing this, — by radiation and by evapora- 
tion. The body is thus constantly producing and is as constantly losing heat. Its 
actual temperature is certain to be something above that of the surrounding medium, 
— how much will depend upon the relation between the rapidity of production 
and the facilities for radiation and evaporation. The body temperature is thus a 
kind of algebraic sum, and it depends upon a great variety of conditions. Small 
animals radiate rapidly, large ones less rapidly, for radiation is a surface action, 
and their surface is less in proportion to the bulk. Hogs radiate slowly, because 
of their blanket of fat. They do not sweat, and thus are easily overheated. 



EXTERNAL INFLUENCES AS CAUSES OF VARLVl'ION 23 I 

Water, or the lack of it, is therefore in many countries and in 
many seasons the limituig element ; that is to say, the yield is 
limited not by the available fertility or the ability of the crop but 
by the moisture present. 

In excessively wet seasons crops are notoriously " soft," that is, 
lacking in substance. Just what the difference is has not been 
well established, but size has been attained at the expense of 
quality. There is good reason to assume that it is the result of 
abundance of water, leading to full cellular development, but 
deficiency of evaporation and transfusion of food due to cloudy 
skies, resulting in a lack of actual dry matter. 

Effect of moisture in the atmosphere. It is said that moist 
atmospheres produce fineness of hair or fur in animals and deli- 
cate foliage in plants, and that a dry atmosphere inclines to a 
harsh, dry coat and to spiny growth in plants. Under natural 
conditions, however, moisture is often associated with coolness and 
shade, and dryness with great heat and intense light. Certain it 
is that fur-bearing animals are found in cool climates and that 
vegetation is delicate in the temperate region but harsh, dry, 
and spiny in the arid sections. These facts are well known and 
universally recognized, but how much is clue to moisture alone 
cannot well be determined in nature. 

Resorting to direct experiment, however, we find that the same 
plant may be grown with or without spines according to the 
degree of moisture in the surrounding atmosphere. Spines are 
undeveloped leaves, as thorns are abortive stems, and anything 
that checks growth tends to their production. That this is mainly 
the result of a dry atmosphere, however, is easily shown in the 
laboratory. 

** Lothelier has made numerous observations in which individ- 
uals of the same species were placed side by side, some exposed 
freely to the air and others kept moist under a glass shade." 
Under conditions such as this " Berberis vulgaris bore non- 
spinescent leaves in a moist atmosphere, but spines alone in a 
perfectly dry one. Again, the shoots which in Lychim barbarum, 
Ulex Eii7-opcBus, etc., would normally have formed thorns, by 
arrested development and sclerosis (hardening), in a very damp 
atmosphere continued to grow, and elongated into leafy branches." 



232 



CAUSES OF VARIATION 



Microscopical examination showed that in the dry-air specimens 
" the palisade cells were well developed and there was a special 
consolidation of fibrous tissues." ^ The same author continues : 

Again, the common water reed PJiraginites coz/n/nt/iis, when growing in 
the unirrigated areas of the Nile valley, forms a stunted growth with very 
short and sharp-pointed leaves. Close to the Nile, however, ... it grows 
nine or ten feet high, with long leaves almost exactly like the plants in 
English rivers. 

All observations go to show that the number of vessels in the 
fibro-vascular system is greater in the aerial than in the aquatic 
forms of the same species,^ and the evidence in general seems 
conclusive that the notorious abundance of spines in tropical 
vegetation is due primarily to a dry atmosphere, assisted to 
some extent, no doubt, by the retarding effect of intense light 
upon growth. 

A significant fact in this connection, possibly attributable to 
the scarcity of water, possibly to the lack of heat, is the well-known 
phenomenon that plant lice, producing females only during the 
summer, begin with approaching autumn to produce males, and 
that under the perpetual heat of the greenhouse the insects ob- 
serve summer habits indefinitely unless the plants on -cuhich they 
are feeding are allozved to become dry. 

As is well known, seeds may be kept for long periods if 
thoroughly dried. In this case the vital activities are reduced to 
a minimum, but probably not entirely suspended, because seeds 
will not last indefinitely. Certain lower forms of plant and ani- 
mal life have a marked power of apparently suspending life 
through desiccation and resuming its activities again with suffi- 
cient moisture.-^ 

The actual influence of water upon development is not yet 
well understood, except that it is one of the absolute conditions 
of life, and, being a fluctuating element, often limits development. 

The student should fully appreciate the bearing of all this upon 
the matter in hand : The degree of development of an individual 
at maturity is not a complete index to his inherited characters. 

1 Vernon, Variation in Animals and Plants, p. 264; see also Henslow, Origin 
of Plant Structures, p. 40. ^ Vemon, Variation in Animals and Plants, p. 265. 

3 C. B. Davenport, Experimental Morphology, Part I, pp. 59-65. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 



^33 



It is both something /ess and something more. It is /ess by so 
much as the individual has failed to develop because of unfavor- 
able external conditions ; it is more by whatever development is 
due to the c/ireet influence of external conditions. 

This is the principal reason why breeders have difficulty in 
knowing how much to credit to inheritance, and it is on this 
account that more knowledge is needed of the nature and extent 
of the development due directly to external causes, and therefore 
independent of inheritance. After all, however, it will be found 
that the total development from all causes is well within hereditary 
limits except, perhaps, in rare cases where the normal functions 
may have been altered by unusual conditions. 

SECTION IV — EFFECT OF CONTACT UPON PROTOPLASMIC 

ACTIVITY 1 

Unstable chemical compounds are exceedingly sensitive to 
mechanical contact either from solid bodies or from liquids or 
gases in rapid motion. Davenport says:^ 

Mechanical disturbance can induce in certain lifeless compounds violent 
chemical changes. Compounds which are so affected are preeminently 
unstable. This instability, however, varies greatly in degree. In some 
cases the blow of a hammer is required to upset the molecules, the result 
being often a violent explosion. In other cases (e.g. chloride or iodide of 
nitrogen^) the slightest touch of a feather suffices to produce an explosion. 
Now, most of the substances which explode upon impact [altering their 
chemical arrangement and properties] . . . are organic compounds, — 
fulminate, nitroglycerin, gun cotton, and picric-acid derivatives, — and 
therefore it is not surprising that we find the notoriously unstable proto- 
plasm violently affected by contact. 

" Of special interest in this connection " is the fact that 
'^ periodie disturbances produce very important molecular changes 
in [certain] chemical compounds. Certain substances have a 

1 C. B. Davenport, Experimental Morphology, Part I, pp. 97-110, and Part II, 
pp. 370-388, from which most of the data on this subject are taken. N. B. Con- 
tact agents are technically known as molar agents. 

2 Ibid. Part I, pp. 97-9S. 

^ When chemical terms of this kind are used outside of quotations the new 
form will be used, as nitrogen chlorid, omitting the c. 



2 34 



CAUSES OF VARIATION 



specific rate of vibration, so that when this is reproduced by a 
vibrating cord or plate, explosion of the substance may occur, 
lodid of nitrogen is one of these substances which is exploded 
by a high note." ^ Living protoplasm is no exception to the 
general rule that specially unstable compounds are sensitive to 
contact. 

Effect of contact upon the metabolism of protoplasm.^ It is a 
well-known fact that phosphorescence is increased by mechanical 
irritation. So true is this that the water thrown from the pro- 
peller wheels of a steamer in tropical regions looks like liquid 
fire, and a brisk breeze moving over the .surface suggests at a 
distance the white foam of the surf. 

Contact also exerts a strongly stimulating influence upon secre- 
tions, not only with lower organisms which seek attachments, and 
the glands of insectivorous plants, but with higher animals as well.^ 

Effect of contact upon movement. The first effect of mechanical 
disturbance in protoplasm is to check all movement. Minute or- 
ganisms, tradescantia hairs, etc., cease their protoplasmic motion 
by the irritation of mounting under the cover glass. In higher 
plants a sudden jar causes cessation of movement and often a 
retreat of the protoplasm to one side of the cell so characteristic 
as to be spoken of as "fright." 

If an amoeba with pseudopodia out is touched or irritated, it 
immediately assumes the spherical form, and in general the effect 
of contact is to cause protoplasm to cease motion and assume 
approximately the spherical form, or, in other words, to occupy 
the least space possible. But this is to all intents and purposes 
contraction, and the general principle may be laid down that ex- 
ternal contact causes contraction, especially noticeable in muscle, 
which is par excellence the cojitractile tissue. 

This contraction most commonly, and of necessity, operates 
at first to draw the organism azvay from the irritating body 
(negative thigmotaxis), but if the body be long or large, so that 
locomotion continues, then the side next the foreign body will 

1 This suggests, as the author observes, the phenomena of hearing. 

2 C. B. Davenport, Experimental Morphology, Part I, pp. 98-99. 

3 As is well known, the heifer that has never produced a calf may be made to 
give milk merely by persistent manipulation of the udder. 



EXTERNAL INFLUENCES AS CAUSES OF VARLA.TION 235 

be shortened and the organism will move in a curve that will 
speedily bring it into actual contact. It is noticeable, too, that 
real contact, being once established, is broken with difficulty. 
Many lower animals, as in aquaria, coming in contact with a plain 
surface, move along that surface until they reach a point where 
side and bottom or where two sides join, and where they can 
place their bodies in contact with two surfaces. They are likely 
now to move along the groove formed by the two surfaces until 
a corner is reached where contact on three sides is possible. 
Here, if anywhere, the organism will come to rest. It is only 
that it is " more comfortable " ; that it moved under the molar 
impulse until it reached a point where further movement and 
more complete contact were alike impossible. Even higher 
animals come to the highest state of rest when in contact with 
foreign bodies on as many sides as possible. 

Effect of contact upon direction of movement, — thigmotaxis, 
or stereotropism.^ It is a well-known fact that roots growing in 
running water grow upstream, not downstream, and that many 
fish at the breeding season are possessed of an irresistible im- 
pulse to move against the current (rheotaxis).^ They therefore 
ascend the strongest currents, leap waterfalls, and surmount 
every possible obstacle in upstream movements, — a passion 
which ultimately carries them to their breeding grounds in shal- 
low water. It is at these times that salmon pile themselves up 
even above the water level and that they will follow any decoy 
that leads against the current, even into hopeless traps. 

Thus may external agents exert a strongly modifying influ- 
ence upon such essential activities of living matter as the 
contractility of protoplasm, resulting in definitely directed move- 
ments through their control of muscular contraction. As we 
shall see, contact is not the only influence capable of stimulat- 
ing contractility of protoplasm and controlling the direction of 
movement ; on the other hand, muscular tissue is exposed to 
the exciting influence of a great variety of circumstances both 
internal and external to the organism, any one of which will 
induce the characteristic reaction of this sort of tissue, which is 
contraction. 

^ C. B. Davenport, Experimental Morphology, Part I, p. 105. ^ Ibid. p. 109. 



236 



CAUSES OF VARIATION 



SECTION V — EFFECT OF GRAVITY UPON LIVING 
MAlTERi; GEOTROPISM^ 

A germinating seed sends out two sprouts. From whatever 
position they emerge, one grows downward in response to grav- 
ity, the other upward in opposition. In other words, the root is 
positively and the stem is negatively geotropic ; that is to say, 
each contains within itself some quality that 
puts it into definite relation with the center of 
the earth, but in opposite directions. 

That this tendency is something consider- 
able is shown by the fact that it is capable of 
e.xertion against pronounced resistance, as in 
burrowing through the soil or persisting against 
mechanical obstructions. 

This definite relation to gravity seems to ex- 
ert itself in the manner of inward forces respond- 
ing to outside conditions ; for if a piece of 
stem be altered in its position, future growth 
readjusts itself as promptly as possible in 



1 C. B. Davenport, Experimental Morphology, Part I, 
pp. 1 12-124 ; 'ilso P^i't II) PP- 391-402, from which mostof 
the facts here cited are taken. 

2 Two series of terms are in use, of substantially the 
same meaning: one (see "geotropism" and "geotropic"), 
with endings derived from the Greek meaning to turn ; the 
other (see "geotaxis" and "geotactic"),with Greek endings 
signifying to arrange. We thus have also "chemotropism," 
with its adjective " chemotropic," over against " chemo- 
taxis," "chemotactic," " heliotropism," and " heliotactic," 
etc. The latter endings were supplied when the effect of 
chemicals, gravity, and light upon free-tti.ovmg organisms, 
as bacteria, swarm spores, etc., was first noted, which effects 
led to definite " arrangements " ; but when similar effects 
were noted upon larger organisms not free to move, like 
the fixed plants, but which manifested the effect by turning, 
the term " tropism " came into use, signifying a turning. 
This term and its derivatives seem to express more accu- 
rately what really happens in most cases, and they are 
coming to be preferred in all generalized considerations. 
Hence in the text the term " geotropism " is preferred to 
" geotaxis " and similarly in most places for all correspond- 
ing terms. 




Fig. 25. Influence of 
geotropism : be- 
havior of a grow- 
ing plumule in 
righting itself after 
being placed in a 
horizontal posi- 
tion, as at I. — 
After C.B. Daven- 
port, from Stras- 
burger 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 237 

accordance with this inward polarity and the new conditions 
(see Figs. 25 and 26). 

Vochting's experiments as here figured, and as described by 
Morgan,^ indicate that the formation of stem or of root is a 





E 

Fig. 26. Influence of polarity and of gravity upon the character and direction of 
growth. — After Morgan, from Vochting 

A, piece of willow (cut off in July) suspended in moist atmospher?, with apex upward ; B, 
older piece of willow (cut off in March) suspended in moist atmosphere, with apex 
downward ; C, piece of willow with a ring removed from the middle, apex upward ; 
D, piece of root of Popiilus dilafafa, with basal end upward ; shoots from basal 
callus ; E, piece of root of same with two rings removed ; new shoots develop from 
basal callus and from basal end of each ring 

question of both internal causes (polarity) and external influ- 
ences (gravity), that is to say, the character of growth is a func- 
tion both of internal and external conditions. 



1 Morgan, Regeneration, pp. 72-83. 



238 CAUSES OF VARIATION 

A stem of willow severed from its parent plant and suspended, 
apex upward, in a moist atmosphere, will of course send out 
shoots from its apex and roots from its base. If a ring of bark 
be removed from the middle of the stem, then sprouts will issue 
from the apical extremities of the sections and roots from the 
basal end. Neither of these experiments determines whether 
gravity or polarity is chiefly instrumental in the production of 
stem and root, but if the piece be inverted and suspended apex 
downward (in a moist atmosphere), we shall get some light on 
the two forces, external and internal. 

Under these conditions the apical end, now downward, will 
yet produce stems, but they will change their direction with ref- 
erence to the axis and point tipivard, while the basal end will 
produce roots, but they will extend downward. In this case 
each end has produced its characteristic growth, and each has 
responded to gravity in the usual way (see Fig. 26), except that, 
if the piece be of the older wood, roots will appear throughout 
the entire length. The force that fixes the character of growth 
appears to be internal ; that which fixes its direction appears to 
be mainly external. 

If a begonia leaf be planted in the ground or suspended in 
moist air, whatever its position roots will start from the basal 
end of the stem at its point of severance, and afterward shoots 
will arise just above the point of origin of the roots, the body of 
the leaf withering away.^ (By "above" is meant between the 
origin of the root and the apex of the leaf, whatever its position.) 

By this we see that the stem has a distinct polarity, producing 
sprout and root, each at the proper end ; that the leaf has no 
true polarity, producing primarily only roots ; but that wherever 
and however produced, a distinct geotropism characterizes both 
stem and root. 

There is little geotropism in leaves, or in the horizontal stems 
of many plants running along or just below the surface of the 
ground. However, the stems and roots produced at the nodes 
of these underground stems are both geotropic. 

Geotropism in animals. Geotropism is much less marked with 
animals than with plants. We may say that only fixed organisms 

1 Morgan, Regeneration, pp. 74-76. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 239 

would be likely to develop decided geotropism ; or, conversely, 
we may say that organisms with marked geotropism would be 
likely to become fixed. In either event less geotropism would be 
expected among animals, and either assumption would square 
with the facts. Many lower organisms truly animal are distinctly 
geotropic, however, and most animals show a decided preference 
as to position with reference to gravity. Both with land animals, 
high or low, and with fish as well, the ventral side is carried 
downward, and the anterior portion in general upward. 

Effect of geotropism upon protoplasm. The protoplasm of cells, 
plant or animal, is not homogeneous. The nucleus is heavier 
than the cytoplasm, and together with chlorophyll granules and 
starch grains tends to settle to the lower side of the cell, giving 
it a kind of polarity due to gravity. " In many ova the yolk 
sinks to the lower pole and the cytoplasm floats on top, in 
whatever position the egg may be held," — a fact which 
" undoubtedly has an important effect upon development." ^ 

General effect of gravity upon development. There is no room 
for doubt as to the profound effect of gravity upon development. 
However, this influence of gravity has been continual and con- 
stant on all existing species for untold generations, and it may 
be looked upon as having already exerted the maximum of its 
influence upon all forms of life. 

The effect of gravity upon development has, therefore, long 
ago reached the position of a constant force to be reckoned with, 
and is now to be regarded as a fixed factor in development rather 
than as a present cause of individual deviation, — to be studied 
more for the sake of learning the degree of dependence of liv- 
ing matter upon outside forces rather than as a direct means of 
further change. 



SECTION VI — EFFECT OF LIGHT UPON LIVING MATTER 

In all chlorophyllaceous plants the amount of carbon fixed, 
and therefore the total of growth in the sense of increase in dry 
matter, is in almost direct proportion to the expanse of leaf sur- 
face and the amount of light that falls upon it. 

1 C. B. Davenport, Experimental Morphology, Part I, p. 114. 



240 CAUSES OF VARIATION 

Light has other influences, however, than those exerted 
through the fixation of carbon. For example, strong sunUght 
tends to check growth in the sense of increase in bulk, and when 
these two effects of light are combined, as they are in the 
tropics, they give us naturally the slow-growing, generally small, 
and extremely dense wood of the lower latitudes. 

Briefly, light, like gravity, exerts specific effect upon matter. 
Many of the effects of gravity (positive geotropism) may be 
regarded as arising from the elementary properties of matter, 
for naturally all matter is attracted by, and approaches as nearly 
as possible to, the surface of the earth ; that is, matter in general 
may be said to be positively geotropic. Sensitiveness to light, 
however, should be regarded as due to the special compounds 
that constitute living matter, rather than as a property of mat- 
ter in general, for matter in general is indifferent to light. 

Light exerts influence upon living matter, especially plants, in 
three distinctly different ways : (i) through its heat rays, affect- 
ing temperatures ; (2) through the so-called chemical (actinic) 
rays, causing definite chemical reactions in the protoplasm ; 
(3) through the luminous rays, influencing especially the direction 
of growth in those parts that are so fixed as to be incapable of free 
movement. Certain of these influences are worthy of somewhat 
extended consideration. 

Chemical effects of light. ^ While matter in general in its 
simpler compounds is quite indifferent to light, yet certain com- 
pounds are notoriously dependent upon its influence ; that is 
to say, many combinations are effected more readily and others 
only in the presence of light (photosynthesis). 

Oxidation of vegetable oils is much more rapid in daylight 
than in darkness. Hydrogen and chlorin unite explosively in 
tJic presence of light. Chlorin passed through alcohol in strong 
sunlight unites with it, forming chloral hydrate, and chlorin 
compounds generally are sensitive to light. 

The whole field of photography is dependent upon the action 
of light upon the halogen salts of silver, gold, platinum, and 
other metals, due to the so-called "chemical rays" extending 

^ C. B. Davenport, E.xperimental Morphology, Part I, pp. i6i- 165, from which 
most of the instances under this heading are taken. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 24 1 

from the blue upward and most pronounced in the invisible 
"ultraviolet" portions of the spectrum. These particular wave 
lengths seem closely akin to chemical energy, and their effect, 
invisible and subtle as it is, should not be overlooked. 

Certain organic compounds are readily formed only by the 
aid of light ; thus the reaction Cj4Hg02+CgH5CHO=Ci4H8 
(O.H)(O.CO.CgHj;) takes place in sunlight, but in darkness the 
substances are indifferent to each other. ^ It is under this same 
principle that the vegetable substance chlorophyll is able to 
break up the CO.2 of the atmosphere and fix the carbon in the 
form of starch, setting free the oxygen. This is the most dis- 
tinctive act of plant life, and yet it takes place only in the pres- 
ence of light. The student is therefore prepared to realize that 
light is one of the controlling forces, not only in effecting 
chemical compounds in the non-living world but in the activi- 
ties of living matter as well ; that in many respects its action is 
fundamental (as in the fixing of carbon), in others incidental, 
and in still others even accidental (as in the color of chloro- 
phyll or of gold or silver). In any event it is an influence to 
be taken account of when one is engaged in the study of the 
circumstances that control the activities of living matter. 

Effect of light upon functional activity.'^ The effects of sun- 
light upon growth are of three kinds, — one due to the heat 
rays of the lower spectrum, the others to the luminous and the 
so-called chemical or "actinic" rays of the upper spectrum, from 
the blue to a considerable distance beyond the violet. Strange 
as it may seem, the influence of light upon the fixation of car- 
bon is greatest in the thermic rather than in the actinic region 
of the spectrum. Timiriazeff^ kept a plant in the darkness 
until the starch in the leaves had been absorbed. " Then in a 
dark room a prismatic spectrum was thrown upon the leaf and 
the position of Fraunhofer's lines indicated on the leaf. After 
three to six hours starch had formed under the influence of the 
light, only in the region of the absorption baruis of cJiloropJiyll 
lying between B and D^' as determined by treating first with 

1 C. B. Davenport, Experimental Morphology, Part I, p. 163. 

2 Ibid. Part I, pp. 166-180 ; Part II, pp. 416-436. 

3 Ibid. Part I, pp. 169-170. The italics are mine. 



242 CAUSKS C)K \ARIAT10N 

alcohol to decolorize, and then with iodin, which forms its char- 
acteristic blue with starch. The sjxxnrum between /> and D^ 
includes the upper part of the red, the orange, and the lower 
parts of the yellow. — the thermic rather than the actinic 
portion of the spectrum. 

Among both plants and animals light has an important influ- 
ence upon color. The chlorophyll of plants is formed only in 
its presence, and it is intimately concerned in the production of 
pigments in the skin. Not only that, but the arrangement and 
position of pigmentary matter, whether lying next the surface 
and well diffused — thus giving color to the animal — or lying 
collected in masses deeper in the skin and having little effect 
upon the color, are due largely to the direct effect of light 
falling upon the skin of the animal. In this way certain animals, 
as the chameleon, are capable of e.xhibitinga considerable range 
of colors, giving rise to the fiction that they are able to imitate 
any color near which they may be situated."^ 

It has been customary to cite the fact that cave animals are 
frequently less highly colored than their congeners of the land, 
as evidence that color is fundamentally dependent upon light. 
This cannot be tRie except in a very general sense. All material 
substances have some relation to light and therefore have some 
color. What the color of a body may be is therefore dependent 
primarily upon its composition, and in this sense its color may 
be said to be accidental, — a remark that is as true of chlorophyll 
as it is of gold or silver, or of red, white, or yellow brick. 

But when the particular compound happens to be one like 
chlorophyll, or a pigment that can be fanned only in the presence 
of light, then and then only can color be said to depend upon 
the presence of light. Deep-sea fishes are often highly colored ; 
rocks hidden in the earth have their characteristic tint ; the 
blood of vertebrates is reil. not from the presence of light but 
from the presence of compounds of iron. In all these cases 
the color arises from a substance in no sense dependent upon 
light for its formation and existence, and the case is distinct 

^ The vibrations at this point are approximately 5-5 x 10^* per second (525»- 
000,000.000,000). 

- C. B. Davenport, Experimental Morphology, Part I, pp. 192-194. 



ICXTIoKNAL 1NFLU1<:NC"I;S as CAUSl'lS Ol- VARIATION 243 

fi'oni one ill which the color is due to ;i subsliince lornied only 
by the aid of li,i;hl. It is only in this latter case that li^ht- 'ii'iy 
truly be said to be a direct external cause of variation. 

Examples of this are found in the coloring of fruit, either 
under normal conditions or in " fruit photography," a process 
by which pictures may be made to api)ear on iiighly colored 
fruit by shading with a screen derived like a negative from the 
picture to be transferred.^ 

The sun is supi)osed to exert a direct effect upon the skin, 
ranging from the tan of the white man to the dark color of the 
tropical races. This seems an ill adaptation, and so it is as 
regards the heat, for black objects are warmer than white ones ; 
but the adaptation is not to the heat rays but to the chemical, 
for black pigment is almost totally non-actinic. Hence we may 
say that dark-skinned people have lost something in heat resist- 
ance, but they have gained what is of more conse(|uence, — a 
screen against the actinic rays.^ 

Light exhibits its most characteristic effec^t uiv)n the eye of 
higher animals. It here gives rise to two remarkable actions, — 
muscular contraction of the iris, by which the amount of light 
admitted is regulated, and a nerve stimulus, which forms a defi- 
nite image on the retina, as upon a mirror, and which is perfectly 
compreiiended by the mind. Whether the colors and images 
seen by all eyes are absolutely identical is obviously a matter 
that can never be determined. It is of course safe to assume 
that the images, in so far as fonn is concerned, are identical, 
because the outlines are due to the mechanical laws of refrac- 
tion, but the colors as comprehouied may be due in part, if not 
entirely, to physiological peculiarities. That is, the color which 
to one is red may look to him as yellow does to another, — a 
supi)osition entirely ])lausible when we remember that with 
some individuals sound always suggests color as well, so that 
the name Jones immediately suggests black, or red, or some 
other color, differing with different individuals. What relation 
or coordination between the auditory and the optic nerves can be 
responsible for this sort of mixed impression we do not know. 

1 Lilcrary Digest, Septeml)er 16, 1905, \). 381. 
- Ibid. October 7, 1905, p. 485. 



244 



CAUSES OF VARIATION 



Vital limits. Chlorophyllaceous plants are absolutely depend- 
ent upon light for their very existence, but parasitic plants, 
and animals in general, are not dependent upon light in any 
vital sense, because they, like animals, subsist upon highly 
organized materials in which the fixation of carbon has been 
already accomplished by other organisms.^ 

All known facts indicate that animal life in general is essen- 
tially successful in total darkness. Mules have been kept in 
mines for twenty years, and beyond temporary sensitiveness of 
the eyes no effect was perceptible. Prisoners have spent their 
lives in dungeons. All embryonic development in mammals takes 
place in the total darkness of the mother's body. It is doubtless 
not too much to say that light has no effect whatever upon the 
vital functions of the higher animals ; that it is as unessential 
in this respect to animals as it is indispensable to plants. 

Bacteria, as a rule, not only do not need the light, and flourish 
best in darkness, but strong sunlight is almost uniformly and 
quickly fatal ; indeed, direct sunlight is recognized as one of 
the most successful germicides (which is of itself the principal 
reason why plenty of light should be provided wherever domestic 
animals are kept). This fact is illustrated by inoculating a gela- 
tin plate uniformly with bacteria, as Bacillus antliracis, covering 
the plate with a piece of black paper out of which some pattern 
is cut, as the letter E, and exposing it all to strong sunlight for 
a few hours. If the plate is then put into an incubator the bac- 
teria will grow, except over the area exposed to the light, in 
which area they have been killed.^ From the well-known fact 
that bacteria i?i a vacuum are not affected by light we conclude 
that death is due to oxidation in the presence of light, a phe- 
nomenon common in organized compounds. 

Light rigor. The movements of protoplasm in general are 
retarded, or even stopped, in the presence of intense light, 
so that rigor precedes death. There is therefore (for plants) 
an optimum, minimum, and maximum intensity, and between 

1 This is written in general terjus, and regardless of the fact that certain 
lower organisms, whose nearest relatives are distinctly animal, themselves bear 
chlorophyll. 

2 C. B. Davenport, Experimental Morphology, Part I, pp. 171-172. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 245 

these limits protoplasm is stimulated by sudden changes, rapidly 
becoming accustomed, however, to alterations within a narrow 
range (phototonus), and soon resuming its normal activity, 
except that as the intensity approaches the point of rigor activ- 
ity appears to be permanently checked. 

Retarding effect of light upon the rate of growth. To the 
higher organisms generally, sunlight, however intense, is not 
fatal, but it not infrequently retards the rate of growth, espe- 
cially among plants. This accounts for the relatively flower 
growth of tropical vegetation as compared with that of higher 
latitudes, and for the fact that growth in the sense of increase 
in bulk is more rapid at night than in the daytime. Sachs 
found 1 that the curve of growth reached its greatest height at 
daylight, then commenced to decline, reaching its minimum a 
little before sunset. Davenport points out that this fluctuation 
is opposed to the effects of temperature, which is more favor- 
able in the day than at night, so that the final results are some- 
what less than the total influence due to light. 

This fact is well illustrated in experiments upon seedlings, 
grown both in darkness and in light, — investigations that are 
entirely feasible, because at this stage the young plant depends 
upon the old seed for its nourishment. It is invariably found that 
seedlings grown in the darkness have grown at the faster rate. 

That different rays have different effects upon the growth of 
plants is easily shown. Flammarion cultivated sensitive plants 
for three and a half months (July 4 to October 22) in red, green, 
white, and blue light. At the close of the experiment the plants 
had attained heights as follows : in the red light, 420 mm. ; in 
the green, 152 mm. ; in the white, lOO mm. ; and in the blue, 
27 mm., with general appearances shown in Fig. 27. 

In this experiment the greatest heat rays were of course trans- 
mitted with the red light, but the general temperature was regu- 
lated by currents of air passing through the various chambers.^ 

It has been roughly stated that light has no effect upon 
germination. In general this is true, though careful experiments 
indicate that most seeds germinate slightly earlier in darkness 

^ C. B. Davenport, Experimental Morphology, Part II, p. 421. 
2 Ibid. pp. 427-429. 



246 



CAUSES OF VARIATION 



than in light, and a few, prominent among which are the poas, 
germinate more readily in the light, as do also the spores of ferns 
and the seeds of the mistletoe.^ 

Evidence as to whether sunlight influences the growth of ani- 
mals is inconclusive. Experiments have been conducted with 
tadpoles, snails, the eggs of certain fish, and with the young of 
higher animals, but while slightly better growth is reported 




Red 



Cireen 



White 



Blue 



Fig. 27. Effect of light upon rate of growth : sensitive plants grown for three 
and a half months in red, green, white, and blue light. — After C. B. Daven- 
port, from Flammarion 

during daylight, it is not certain that other conditions did not 
contribute to the results.^ Experiments in feeding fattening ani- 
mals in darkness and in light fail to establish special differences. 
All considerations point to the conclusion that light exerts a 
strongly modifying influence upon living matter in general, but 
that the higher animals are substantially free from its direct 
effect except to some extent in the matter of color. 

1 C. B. Davenport, Experimental Morphology, Part II, pp. 419 and 424. 

2 Ibid. pp. 425-426. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 247 

Influence of light upon the direction of locomotion or of growth ; 
heliotropism. Irritability to light is one of the properties of 
protoplasm. This reaction is generally in the form of contrac- 
tion, as with muscle fiber ^ resulting in a shortening of the side 
next the source of light. With free-moving plants and animals 
this gives direction to locomotion, and they gradually swing 
about until both sides are equally lighted, when, if motion 
continues, the creatures will of necessity progress toward the 
light. This is positive heliotropism. Quick-moving forms are 
often carried into the source of light by their very impetus, 
before the repellent effect of great heat has time to act. In 
this way moths fly into the candle and are killed, while slower- 
moving forms are checked by the heat in time to save them- 
selves. In this latter case the future movements will be a 
resultant of the positive heliotropism and negative thermotrop- 
ism, by which the insects are held at a certain radius circling 
about the source of both light and heat, as if not able to leave 
it, as indeed they are not. 

Negatively heliotropic forms, like earthworms, are those whose 
protoplasm does not contract in the presence of light, but, on the 
contrary, expands. These are carried away from the light, and 
if, in their wanderings, a lighted area is approached, they are 
unable to enter it. 

When the organism is not free to move, as in the case of 
stems of higher plants, the effect will be manifested in the direc- 
tion of groivtJi^ which is all the response to heliotropism pos- 
sible under the circumstances. In cases of this kind the stem 
will bend toward, or away from, the source of light, according 
as the plant is negatively or positively heliotropic, until all 
sides are equally lighted, in which position it will remain during 
growth, as do other forms during locomotion. 

This placing of the body (or stem) with reference to the 
various " tropisms " is technically known as "orientation," and 

1 As most of the examples to follow are confined to the lower animals, and to 
plants in which protoplasm is comparatively exposed, it is well to remind the 
student that the higher animals are not destitute of the same properties, and that 
they have one exposed region peculiarly sensitive to light, namely the iris of the 
eye, whose muscles contract promptly under its influence. 



248 CAUSES OF VARIATION 

this particular orientation with reference to the rays of light, 
whether parallel to their direction or transverse, has received 
the special name of " phototaxis." ^ 

Effective rays. All experiments indicate that the blue rays 
are the effective ones in producing heliotropic effects.^ Some 
organisms seem sensitive to the yellow, but both red and ultra- 
violet are alike inoperative. Heliotropism is therefore an effect 
decidedly due to the luminous rays. 

Contributary conditions.'^ Heliotropism is dependent upon a 
variety of conditions both external and internal to the organism. 

1 There is great uncertainty as to terms. The one just quoted ("phototaxis") 
is in its root a protest against the old term "heHotropism " in that it recognizes 
//i,'/// as the active agent rather than the siin {/lelios), which is a source not only of 
light but of heat and chemical energy as well; and it recognizes, too, that these 
influences are exerted as light, quite independent of the sun or any other particu- 
lar source. 

Of late there has been a strong disposition to substitute this root for the older 
term, giving us phototropisni in place of " heliotropism." Those disposed to this 
view would go farther and discriminate between those movements that appear to 
occur with reference to the direction of the rays, which is " phototaxis," and those 
which are made with reference to the intensity of illttnii nation, which is " photop- 
athy." These students also recognize the fact that irritability and the consequent 
movements, whether positive or negative, depend very much upon the intensity, 
so that organisms that are negatively heliotropic at high intensity are positively 
heliotropic at low intensity, suggesting a middle point at which the organism will 
be held, as with deep-sea animals that come near the surface at night but sink to 
considerable depths in the bright light of day, the water acting as a screen. This 
neutral point or satisfied condition is described as "phototonus." 

It may be necessary to recognize all these distinctions when the subject is 
better understood, but it is more than likely that these different behaviors are 
only different manifestations of the same natural irritability to light on the part of 
protoplasm in general, and that the so-called " phototaxis " or even "phototonus" 
is only the condition of the organism after it has brought itself into such position 
that one irritability is balanced by another (which is always easy with bilateral 
symmetry), or that it is a kind of acclimatization acquired by the protoplasm to 
the particular intensity at hand. 

The theoretical objection to direct reference to the sun is certainly sound. The 
attraction (or repulsion) is with reference to light as light, and not to the sun as 
its source. But the sun is preeminently the source of light, and for this reason, 
and with a proper understanding of the facts, the author prefers for our purposes 
to adhere to the single old term, at least under the present state of knowledge, 
for if properly understood it seems substantially correct and serves all practical 
purposes fairly well. 

2 C. B. Davenport, Experimental Morphology, Part I, pp. 201-203; Loeb, 
Studies in General Physiology, pp. 29-31. 

3 Ibid. pp. 196-201. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 



249 



It is first of all dependent upon intensity of light, feeble illumi- 
nation being ineffective, even if the characteristic rays be pres- 
ent. Not only that, but some organisms are positively helio- 
tropic in moderate light and negatively heliotropic in strong 
light. In this way many fishes are held in a nearly constant 
illumination, rising or falling in the water according to the 
intensity of sunlight, and coming completely to the surface at 
nightfall. 

Another element in heliotropism is temperature, its influence 
being most active at the maximum or normal, and lessening or 
disappearing as it falls. 

Still another controlling influence is the condition of the 
animal. Many caterpillars are positively heliotropic only when 
unfed. They are thus led to ascend trees when hungry and to 
descend when filled.^ Still again, certain animals are heliotropic 
only under peculiar circumstances ; for example, Loeb found that 
winged ants exhibited no reaction to light except at the time of 
their nuptial flight, when they were decidedly heliotropic.- 

Influence of light upon the direction of growth.'^ Instances of 
this influence upon the stems of plants are almost too common 
to need mention. The leaning of plants toward the window, or 
of trees over a stream, can be seen almost any day. 

It is noticeable that most leaves appear to be destitute of 
heliotropism, and yet it is not impossible to detect traces of its 
influence. On careful observation it will be noted that some 
leaves tend to present their upper surface at right angles to 
light rays, while others tend to present the edge. 

It is a general principle of orientation that organisms with 
radial symmetry, like most plants, present as nearly as possible 
the end of the long axis to the source of light, with the lateral 
parts equally lighted ; while organisms of bilateral symmetry, 
like most animals, tend to present the dorsal surface at right 
angles to the light, with the oral (head) end nearest its source, 
the right and the left halves equally lighted, and the ventral 
surface shaded. 

1 Loeb, Physiology of the Brain, p. 189. 

2 Loeb, Studies in General Physiology, pp. 52-53. 

3 C. B. Davenport, Experimental Morphology, Part II, pp. 437-445. 



250 



CAUSES OP^ VARIATION 



In the very highest animals little but the eye is sensitive to 
light, most parts being protected by a heavy epidermis or other 
covering, so that heliotropism in its strictest sense is in them 
limited to the visual parts. In lower animals, however, with 
bodies less protected, light exerts a controlling influence upon 
movements. 

Influence of light upon the direction of locomotion.^ It has 
already been explained that some animals exhibit heliotropism 
only at certain periods of their lives, or only in certain condi- 
tions, as when hungry. Others, however, are constantly and 
uniformly sensitive. The common house fly is positively helio- 
tropic, while the larvae of the same, hatched in the dark, soon 
become strongly negative, and so continue while in the larval 
condition.^ 

This difference between the larval and adult stage is common, 
and led Loeb at first to suppose it to be a general principle, — 
a conclusion invalidated by the fact that caterpillars and their 
imagoes behave alike. ^ 

Both moths and butterflies are positively heliotropic, but 
moths are "attuned" to a lower intensity. This, with their 
more rapid flight, is responsible for their wholesale destruction 
by the naked flame, which the slower-flying butterflies avoid as 
a source of heat. 

The tendency of many small animals to creep into crevices as 
if to hide must not be understood as evidence of negative helio- 
tropism, much less as evidence of timidity. It is often due simply 
to contact irritability (stereotropism), for it is a well-established 
fact that living matter is sensitive to contact with other solid 
substances. This is the principle discussed in Section IV and 
the one that generally lies at the basis of the huddling together 
of individuals, or of their crowding into corners or crevices. 
Loeb brought out this principle very nicely with some negatively 
heliotropic butterflies which wedged themselves closely between 
two plates of glass in the presence of light, showing how one 
tropic influence — in this case contact irritability — is competent 

1 C. B. Davenport, Experimental Morphology, Part I, pp. 180-210; Loeb, 
Studies in General Physiology (1905), pp. i-i 14, from which most of the examples 
are cited. ^ Loeb, Studies in General Physiology, p. 20. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 251 

to overcome an opposite but weaker one, — in this case nega- 
tive heliotropism. 

It is a noteworthy fact that irritabihty to Hght, while a prop- 
erty of protoplasm in general, is more pronounced in some cases 
than in others, even within the same organisms. This is true 
not only in the ej/cs of animals, but, in general, the oral (anterior) 
end of eyeless animals is much more sensitive to light than is 
the aboral ; ^ as also is the dorsal surface more sensitive than 
the ventral. Light therefore operates strongly to influence not 
only the position but the locomotion of animals as well. 

The following conclusions from Loeb upon the influence of 
light are valuable.^ In substance they are : 

I. " The dependence of animal movements on light is in every 
point the same as the dependence of plant movements on the 
same source of stimulation." 

1. "The direction of the median plane or the direction of 
the progressive movements of an animal coincides with the 
direction of the rays of light." 

2. " The more refrangible rays of the visible spectrum are 
more effective than the less refrangible rays." 

3. " Light of a constant intensity acts as a constant stimulant." 

4. Heliotropism is in a large measure dependent upon the 
intensity of light, differing for different animals. 

5. " Heliotropic movements occur only between certain limits 
of temperature." 

II. " The orientation of an animal toward a source of light 
depends on the form of the body, just as the orientation of a 
plant to light depends on the form of the plant." 

1. " Symmetrical points on the surface of dorsi ventral animals 
possess equal irritabilities." 

2. The " irritability of the oral pole of an animal is different 
from the irritability of the dorsal pole," and is generally greater. 

3. " The irritability of the ventral surface is different from the 
irritability of the dorsal surface." 

" These three conditions taken together cause dorsi ventral 
animals to place their median planes in the direction of the 

^ Loeb, Studies in General Physiology, pp. 76-78. 
2 Ibid. pp. 81-84. 



252 



CAUSES OF VARIATION 



rays and to move toward or away from the source of light in 
this direction." 

4. " Eyeless animals behave in this respect like animals hav- 
ing eyes." 

III. " Heliotropic irritability of an animal manifests itself 
frequently only at certain epochs of its existence." 

1-4. In winged ants this epoch is at the nuptial flight; in 
plant lice it is when the wings are present ; in the larvae of 
Musca vomitoria negative heliotropism is most prominent when 
the larva is fully grown ; and in a large number of animals the 
irritability is opposite in the larval and in the adult stages. 

5. " Both night and day Lepidoptera are positively heliotropic, 
and their heliotropism is similar to that of every other positively 
heliotropic animal. The period of sleep of the night Lepidop- 
tera, however, falls in the daytime, and only for this reason is 
their heliotropism manifested exclusively at night." ^ 

IV. "In many animals heliotropic irritability is connected 
with sexuality." Ants are sensitive only at the time of the 
nuptial flight, and in both ants and Lepidoptera the males are 
more sensitive than the females. 

V. " The behavior of an animal depends on the sum total of 
its different forms of irritability." 

VI. Many animals are "compelled to orient their bodies 
against the surfaces of other solid bodies," or to bring their 
bodies "in contact with other solid bodies on as many sides 
as possible (stereotropism)." 

VII. Animals " may be forced by light to move from diffused 
light into sunlight and to remain exposed to the high tempera- 
ture of the sunlight, even though it may cause their death." 

Considering all the "irritabilities" and " tropisms " to which 
animals and plants are exposed and to which they react, it is 
not necessary to appeal to instinct^ or even to the nervous 
system^ to explain all movements of animals, nor is it well to 
ascribe to them such anthropomorphic qualities as love of light, 
distaste for darkness, preference, avoidance, curiosity, reason, or 
other such bases of higher intelligent action. 

1 The question naturally arises, Why is the daytime the period for sleep in a 
positively heliotropic animal ? The answer has not yet been given. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 253 



To these conclusions two observations may well be added for 
present purposes : 

I. Heliotropism, like many other reactions of protoplasm, 
arises from the nature of the organism, and not necessarily from 

14:31 



V'" 



ft" 



f.c 



1 10:55 



10:44 



I! 



10:34 
28 



(2). 14:0O to 14:20 
—> 



^■^4 



Interval 
not observed 



13:06 
13:00 



'^ 



I 



12:54 y 



14:21 




(3). 14:20 to 14:34 



Fig. 28. Effect of light upon locomotion : 
movements of an amoeba in response 
to changing directions of light. Ar- 
rows show the direction of the light 
rays, andfigures showthehour(i3= i 
o'clock, etc.). — After Davenport 



f(1). 12:48 to 14:00 



a basis of utility. For example, roots are in general positively 
heliotropic, — a quality that is not of the slightest usefulness, 
and which must be regarded as entirely accidental. Again, this 



254 



CAUSES OF VARIATION 



quality is often fatal, as in the case of moths. In general, how- 
ever, matters have long since become adjusted to these reactions 
as to other necessities governing the behavior of living matter. 

2. All experiments indicate a high degree of variability among 
individuals, not only as regards the degree of response to hcliot- 
ropism, but also as regards the effect of all other outside influ- 
ences, even that of poisons. 

Among examples furnished by the extended investigations 
into this subject, we have space to note but two. 

The amoeba, which represents about the simplest form of 
animal life, is an excellent medium for illustrating sensitiveness 
to light. Fig. 28 exhibits the movements of one of these bits of 
living matter under the influence of light, whose direction, as 
shown by the arrows, was occasionally changed, the figures in- 
dicating the hour, — all of which is strongly suggestive of the 
process of driving sheep. 

The other example to be noted is the effect of light upon the 
position of the chlorophyll granules in the leaf cells, under dif- 
ferent degrees of illumination, whether on the exterior walls, the 
partition, or the interior walls. 

Conditions that determine heliotropism. Some organisms are 
positively heliotropic in one intensity and negatively so in 
another ; some are positive at one temperature and negative at 
another ; some are positive in a certain concentration (of sea 
water) and negative in another, and the general principle may 
be stated that decreasing the concentration has the same effect 
as increasing the temperature.^ It thus appears that the same 
organism can often be made positively or negatively heliotropic 
at will by altering the surrounding conditions of life. 

SECTION VII — INFLUENCE OF TEMPERATURE UPON 
LIVING MATTER 

The relation of heat to living matter is mainly, but not exclu- 
sively, quantitative ; that is to say, the effect of heat is princi- 
pally upon the rate of growth and activity. In general, each 
species has its maximum, above which protoplasm becomes 

1 Loeb, Studies in General Physiology, pp. 265-294. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 



255 



inactive (heat rigor); its minimum, below which all activity 
ceases ; and its optimum, — that point at which growth is most 
rapid. Certain facts in this connection are noteworthy : 

1. The maxima, minima, and optima are not the same for 
different species. 

2. Protoplasm is killed if carried much above the maximum, 
— the organism decomposes and is destroyed. 

3. Temperatures below the minimum are not fatal except in 
the presence of moisture, which, on conversion into ice, destroys 
the structure of protoplasm by the act of expansion. 

4. The optimum at which growth is most rapid is nearer the 
upper than the lower limit. 

5. Both the optimum and the maximum may be raised by 
careful methods involving gradual acclimatization. 

Specific effect of heat upon protoplasm. ^ Beginning at the 
optimum and decreasing both ways to the limits, it may be said 
in general that protoplasmic activity is in proportion to the tem- 
perature. This is true of the amount of oxygen absorbed, of 
carbon dioxid evolved, of chlorophyll formed, and of carbon 
fixed, — in other words, of metabolism. The same is true as 
to movements of protoplasm and its irritability to light, contact, 
or other stimuli. The following table exhibits the number of 
electric shocks per second recjuired at different temperatures to 
produce tetanus in the neck muscles of a tortoise.^ 



Effect of Temperatures upon Animal Activities 





Temperatures 


Shocks per Second re- 

OlIIRED TO produce 

Tetanus 


Tempekatukes 


Shocks per Second re- 
quired TO PRODUCE 
Tetanus 


4°C. 
9°C. 


I 

5 


21°C. 

28° C. 


25 
34 





Effect of heat upon the rate of growth in plants.-^ The relation 
of temperature to plant growth is well shown in the tables on 
the following page.* 

1 C. B. Davenport, Experimental Morphology, Part I, pp. 222-231. 

2 Ibid. p. 230. 3 Ibid. Part II, pp. 450-460. * Ibid. p. 451. 



256 



CAUSES OF VARIATION 



Growth in Millimeters of the Plumules and the Radicles of Seed- 
lings GROWN UNDER DIFFERENT TEMPERATURES FOR 48 HoURS (Sachs) 



Plumules 


Radicles 


Temperature C. 


Maize 


Bean 


Pea 


Temperature C. 


Maize 


Bean 


Pea 


14-16° 








17.0° 


2.S1 




4.0 1 


16-18 


4.6I 


7-4^ 


3,01 


257 




39 




I 8- 20 








26.3 


24.5 


47 




20-22 








28.5 




34 


41.0 


22-24 








1,?>-^ 


390 


30 


17.0 


24-26 








34-0 


55-0 


28 




26-28 


S.6 


II. 


1 0.0 


38.2 


25.2 


22 


12.2 


28-30 








42.5 


5-9 


7 




30-32 
















32-34 


I I.O 


10.5 


5-7 










34-36 


13.0 


15.0 


5.0 










36-3S 
















3S-40 


9i 


10.2 


5-5 










42.5 


4.6 


7-5 













Maxima, Minima, and Optima for Various Species arranged 

ACCORDING TO THE OfITMA ^ 



Sfecies 



Bacillus phosphorescens 

Fenicillium 

Phaseolus multiflorus^ (bean) 
Fhaseolus multiflorus* (bean) 
Pisum sativum •* (pea) 
Sinapis alba* (white mustard) 
Lepidium sativum* . . . . 
Linum usitatissimum* (fla.x) . 

Lupinus albus* 

Hordeum vulgaie* (barley) 
Triticum vulgare* (wheat) . . 

Yeast 

Bacillus subtilis 

Bacterium termo 

Zea mais ■• (Indian corn) 

Zea mais"* (Indian corn) . . 

Cucurbita pepo * (gourd) . . 

Bacillus ramosus 

Bacillus anthracis 

Bacillus tuberculosis . . . . 
Bacillus thermophilus . . . 



Optimum 



20.0" 
22.0 
26.3 
33-7 

26.6 

27.4 
27.4 
27.4 
28.0 

28.7 

28.7 
28-34 

30.0 

30-35 

33-7 
34-0 
33-7 
37-0 
37-0 
38.0 
63-70 



Minimum 



00.0" 

1-5 

9-5 
6.5 
0.0 
1.8 
1.8 

7-5 

5.0 

5.0 

0.0 -f- 

6.0 

5-0 

9-5 

137 
13.0 
14.0 
30.0 
42.0 



2 + 

2 + 

7 
5 
o 
o 

+ 



1 Growth during 96 hours. 

2 C. B. Davenport, E.xperimental Morphology, Part II, p. 454. 

3 Radicle. < Plumule. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 257 

Commenting on this table, its author observes in substance : 

1. That in general the optima, the minima, and the maxima 
rise and fall together ; that is, a species with a high optimum 
will also have a relatively high maximum and minimum. 

2. That species vary greatly ; so much so that the maximum 
of one (/>. phospJiorcscens) may be below the minimum of another 
{B. thcnnopltilits). 

3. That the optimum for the radicle and the plumule may be 
widely apart, as in the bean. 

4. That, in general, the optimum is in close relation to the 
natural habitat of the species, as in B. phosphorcsccns that lives 
in the moderate temperature of the sea, and in B. therviopJiiliis 
that lives in the high temperature of decaying manure. From 
collateral evidence this must be ascribed to acclimatization. 

5. That of all the species noted, the bacteria have the greatest 
range in optimum, showing that they are, as yet at least, less 
fixed in their organization. 

6. That the minimum never falls below 0° C, the freezing 
point of water, which is the minimum for vital activities. 

7. That the maximum temperature tends to be rather constant 
with related species, and among flowering plants the range is but 
9° (37°~46°)- But 46° is a fatal temperature for most proto- 
plasm, and 50° is the limit, showing how near the limit some 
species have been pushed. The extraordinarily high temper- 
atures of B. tJiermopJiilus must be regarded as an instance of 
acclimatization, of which other striking examples are found in 
hot springs.^ 

8. That the range from minimum to maximum varies with the 
species. In this table the range is least for B. tuberculosis (12°) 
and greatest for B. pJiospJiorescens (37°). 

9. That the "wonderful adjustment" of critical temperatures 
to the environment of the species is not to be regarded as 
evidence of selection, but, as is elsewhere shown under "Accli- 
matization," it is due to the modification ivrougJit in the pjvto- 
plasni by the temperatw'e itself. 

1 To the above may be added the observation that the optimum lies nearer 
the upper limit ; that is, the difference between the optimum and the maximum is 
less than the difference between the optimum and the minimum. 



258 



CAUSES OF VARIATION 



Effect of heat upon growth in animals.^ All larger land animals 
have acquired facilities for maintaining practically a constant tem- 
perature. This is not true for all animals, many of which, like 
marine species, are notably dependent for their temperature upon 
the accident of environment, in which respect they differ but little 
from plants. It remains to note, therefore, what influence heat 
may exert upon the growth of animal life so conditioned as to be 
dependent upon the surroundings for its temperatures. 

Increase in Length (Millimeters) of Young Tadpoles of Frog and 

OF Toad, under Different Temperatures, from the 24TH 

to THE 48TH Hour after Hatching ^ 



Temperatures 


Average 


Growth 


Temperatures 

c. 


Average 


Growth 


C. 


Frog 


Toad 


Frog 


Toad 


9-11° 


4-5 


3-0 


23-^5° 




41-3 


11-13 


5-3 


5-3 


25-27 


31-5 


39-0 


13-15 


4-3 (?) 


155 


27-29 


40.0 




15-17 




.6.3 


29-31 


47-5 


56.8 


17-19 


9-5 




31-33 


40.2 


55-3 


19-21 


19.8 


21.2 


33-35 


43-5 




21-23 













Twenty-nine to thirty-one degrees seems to be about the 
optimum temperature for both, from which the table shows that 
the land-living toad prospered rather better under the higher 
temperatures than did the frog, as he certainly suffered more 
under the lower, but that in botJi the rate of growth was sub- 
stantially /;/ proportion to the temperature. 

The author of the table reports that the interval between 
fertilization and hatching in cod varies from thirty days at a 
temperature of — 2°, to thirteen days at a temperature of 6°-8° ; 
that herring vary from forty days at 2°-4°, to eleven days at 
iO°-i2°; and that the time required for the frog to attain a 
development at which the head and tail are sharply defined is, at 
15°, six days ; at 33°, one day. 

1 C. B. Davenport, Experimental Morphology, Part II, pp. 457-460. 

2 Ibid. p. 457. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 259 

Birds develop only at high temperatures. The normal tem- 
perature for the chick is 38°. Fere^ incubated at temperatures 
varying from 34° to 41°. The individuals were all examined at 
the same absolute time, and the following figures express the 
percentages of development attained, taking that of 38° as the 
standard : ^ 



Temperature . . . . 
Index of development 



34" 
0.65 



35^ 
0.80 



36° 

0.72 



38° 
1. 00 



39^ 
1.06 



40- 



41" 
1.51 



The author remarks that some doubt attaches to the figures 
under 35°, 36°, and 37°, and calls our attention to the fact that 
somewhere not far above 41° the series would become zero. 
But for the range given, the development is in proportion to the 
temperature, although the highest given (41°) is considerably 
above that attained under natural conditions. The groiving cJiick 
therefore does not, in nature, achieve its optiminn. 

Effect of heat upon the direction of growth, — thermotropism.'-^ 
Without going into the methods of investigation, it appears that, 
independently of the influence of light or other " tropisms," plants 
are often positively or negatively thermotropic largely according 
to temperatures. The plumule of seedling maize, for example, 
is known to be positively thermotropic at ordinary temperatures, 
while the radicle is positive between 15° and 35°, indifferent at 
37.5°, and negative above. The indifferent point with the bean 
(radicle) is given at 22.5°. 

The subject is little understood, and though the impulse of 
thermotropism is weak as compared with that of heliotropism or 
geotropism, it is supposed to be one which inclines the organism 
to align itself in accord with the direction of heat rays, although 
it is true that thermotropic plants are sensitive to conducted as 
well as to radiant heat. 

Temperature limits of life.'^ All experiments indicate that as 
the temperature rises above the maximum the first effect is heat 



^ C. B. Davenport, Experimental Morphology, Part II, p. 459. 

2 Ibid. pp. 463-467. 

3 For e.xtended discussion, and for tables of temperature limits, see C. B. Daven- 
port, E.xperimental Morphology, Part I, pp. 231-249. 



2 6o CAUSES OF VARIATION 

rigor, which soon passes into death. The more rapid the rise 
the lower the death point, and the more gradual the rise the 
greater the resistance. Again, if the temperature does not rise 
too high, the heat rigor may gradually pass off, and activity may 
be resumed, even at temperatures which at first were followed 
by entire suspension of activity, and even by rigor. This is the 
first stage in the- process of acclimatization. 

Sachs found that a sensitive plant kept at " 40° C. for one hour 
suffered loss of sensibility during twenty minutes after removal. 
Raised slowly to 50°, sensibility was only temporarily lost, but 
52° proved fatal. Immersed in water, heat rigor occurred at a 
temperature 5° to 10° lower." ^ Hofmeister found that hairs 
from the stem and leaf of Ecballiiim agreste, showing lively 
movement, when gradually raised from i6°-i7° C. to 40° C. 
"became motionless," but that "after one or two hours move- 
ment returned and was very violent. Cooled and raised again to 
45° C, the protoplasm was motionless at first, but after seven- 
teen minutes movements recurred but were not rapid." ^ 

The vital limit varies greatly with the species. Thus, roughly 
speaking, for bacteria it is 45° C; for cryptogams, generally 
45°-50°, with an occasional one at 60° ; flowering plants, 
45°-50°; protozoa, 40^-45°, with a few as high as 60°; mol- 
lusks, 30^-40°; worms, 45°-50° (tardigrades, dried, 98°); crus- 
taceans, 26°-43°; insects, 27°-4'3.7°; fish, 27°-40° ; salamander, 
44°; frog, 40°-42°; dog, rabbit, and man, 44°-45°; vertebrate 
muscle, 40°— 50°.^ This series exhibits a wide range of resistance 
to excessive heat, yet few organisms can endure much above 50°. 

All experiments and observations indicate that death from 
high temperatures is caused by coagulation of the albumen of 
the protoplasm, a circumstance showing that albumen carries 
into its vital relations its ordinary property of coagulation by 
heat. That living matter contains many easily coagulable pro- 
teids no longer admits of doubt, and that their coagulation causes 
death is evidenced by the fact that once in this condition they 
do not return to their normal state. 

1 C. B. Davenport, Experimental Morphology, Part I, p. 232. 

2 For full table.s from which these abstracts are made, see C. B. Davenport, 
Experimental Morphology, Part I, pp. 234-237. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 26 1 

Death from low temperatures appears to result from entirely 
different causes. Protoplasm seems to contain no substance but 
water that undergoes either chemical or serious physical change 
by low temperatures. Many yeast cells endure — 1 13.7° C. 
(Schumacher). 

De Candolle subjected " various dry seeds and spores of bac- 
teria to a temperature of nearly — 200°, at which temperature the 
atmosphere becomes liquefied, but without fatal effects." " Cilia 
from the mouth of the frog were cooled to — 90°, and recovered 
their movement upon raising the temperature." " Eggs of the 
frog, lowered slowly to —60°, can revive." From facts such as 
these Davenport concludes that ''there is no fatal teviperattire 
for dry protoplasm} 

The first effect of lowering temperature is a slowing of activity, 
followed, finally, by complete cessation. As is pertinently re- 
marked by the author just quoted, " The fact that cold rigor 
usually occurs close to the zero point (C.) indicates that the 
activities of protoplasms are closely determined by the fluid 
state of water," and " the critical point for vital activity has 
been adjusted to this critical point of water." ^ 

There is much lack of information upon the exact cause of 
death from excessive cold. Among the higher animals the 
immediate cause is without doubt asphyxia from the cessation 
of the blood flow ; but among the simpler organisms the matter 
is not so clear. What evidence w^e have seems to indicate that 
the primary cause of death is in all probability the mechanical 
rupture of protoplasm and cell wall by freezing water expanding 
as it solidifies. 

In any event experience and experiment agree in indicating 
that protoplasm is resistant to excessive cold in the absence of 
moisture, and in all study of this matter we are to remember 
two facts : first, that the freezing point of all protoplasm is 
lower than that of water only ; and, second, that as long as the 
slightest activity is present heat is being produced. From these 
two facts the protoplasm is able to resist actual solidifying much 

1 C. B. Davenport, Experimental Morphology, Part I, pp. 240-242. Though 
not so stated in the text quoted these temperatures are C. 

2 Ibid. p. 242. 



262 CAUSES OF VARIATION 

longer and under much lower temperatures than we should at 
first s«ppose. 

Substantive variation due to temperature ; color markings. 

Early in the section it was remarked that the effects of tem- 
perature are qualitative as well as quantitative. Without doubt 
temperature exerts a controlling influence upon the color of 
butterflies, as has been determined by a number of direct ex- 
periments. 

For example, Vanessa levana and V.prorsa were long regarded 
as distinct species. Levana is " characterized by a yellow-and- 
black pattern on the upper side of the wings," while proi^sa 
" has black wings with a broad white transverse band and deli- 
cate yellow lines running parallel to the margins." ^ Later this 
was recognized as a case of " seasonal dimoj-phism," the yellow- 
and-black levana being the spring brood and the darker prorsa 
being the summer brood ; that is to say, levana, ernerging in 
the spring, breeds immediately, producing a summer brood 
{pT'orsa), and this brood in the same way gives rise to a genera- 
tion which passes the winter in the chrysalis form, emerging in 
the spring as levana. Thus these two " species " are produced 
from the same stock, the difference being that one passes the 
chrysalis stage in the summer, the other in the winter. 

That this difference is one of temperature was proved by 
direct experiment. Dorfmeister ^ succeeded in producing prorsa 
directly from prorsa by the application of warmth to the pupae, 
and " by the application of cold he obtained from levana not 
the pure levana form, but one intermediate between it and 
prorsa^' — an intermediate occasionally observed in nature and 
known as V. porinia? 

Weismann, repeating the experiment, found that by using 
lower temperatures levana could be produced directly from 
levana, and he adds, " The converse experiment was also occa- 
sionally successful, the pupae of the winter generation being 
forced to assume the summer form by the influence of a higher 
temperature during, or shortly after, pupation." ^ 

1 Weismann, Germ Plasm, p. 379. 

2 Vernon, Variation in Animals and Plants, p. 233. 
^ Ibid. ; also Weismann, Germ Plasm, p. 379. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 263 

Here temperature seems to exert a controlling influence upon 
pigment formation, although Weismann is careful to inform us ^ 
that the two patterns " do not correspond " ; that if we were to 
"superpose" one upon the other, "it would seem that the 
black parts in prorsa do not correspond to the yellow ones in 
levana, and that the white band in the former does not corre- 
spond to [either] a yellow or [a] black part in the latter. This 
band is, on the contrary, entirely zvanting in levana, and is 
represented by both black and yellow regions y ^ 

Again, Weismann experimented with Polyommatus pJiloeas^ 
a species " distributed over the whole of the temperate and 
colder parts of Europe and Asia." Toward the north (in 
Germany) the upper surface of the wings is of a "beautiful 
reddish-gold color," hence its popular name, " fire butterfly." 
But he says, " Farther south the reddish-gold color is more or 
less thickly dusted with black, and specimens from Sicily, 
Greece, or Japan often display only a few reddish-gold scales, 
the general appearance being almost black." 

" In Germany this butterfly is double-brooded, and the two 
generations are similar, but in certain districts of southern 
Europe . . . the first generation is reddish-gold, — the second, 
which flies in midsummer and is known as the variety eleiis, 
having the wings well dusted with black." " As in Germany 
during exceptionally hot summers individuals with a blackish 
tint have repeatedly been caught together with the ordinary 
form . . . ," and Weismann observes that it would seem " the 
butterfly becomes red when exposed to a moderate temperature 
and black when the heat is greater." 

Attempts to produce these forms at will, however, by regula- 
tion of temperature only partially succeeded. But the conditions 
were severe. There was no common ancestor. Weismann under- 
took to produce the southern form from the fiorthern stock and 
vice versa. Insects reared from German butterflies but kept in 
high temperatures were in many instances " dusted with black, 
but none of them resembled the darkest forms of the southern 
elens.'' Conversely, butterflies raised in cool temperatures from 

1 Weismann, Genu Plasm, p. 379, 

2 Ibid. pp. 399-4CO, 



264 CAUSES OF VARIATION 

Neapolitan stock were lighter in color than in their native habi- 
tat, but " none were so light-colored as the ordinary German 
form." ^ This difference he ascribes to the cumulative influence 
of the natural seasonal temperatures, and is quick to protest 
against its interpretation as indicating an inheritance of acquired 
characters. He calls it a case of internal selection as between 
"winter and summer determinants." 

However, that is of no consequence in the present connection. 
The facts here given show beyond a doubt that outside tempera- 
tures exert a direct effect upon so important a character as 
color. Whether this occurs by chemical disturbance in pigment 
formation, by internal selection, or by other means does not 
greatly matter here. There is some evidence tending to show 
that the light color of polar animals is due to the direct action 
of cold.^ This, if true, argues for chemical action upon pigment 
as the cause of color changes due to temperature. 

Temperature an all-pervading influence. Temperature differs 
from most other external forces in being, for many species, at 
least, an all-pervading influence. Higher animals and plants 
are themselves centers of heat production, and in general their 
temperatures are the algebraic sum of their own heat production 
and the heat of their surroundings. Lower organisms, however, 
are very largely dependent upon their environment for their 
temperatures, and in cases of this kind the entire protoplasm of 
the body is affected. 

SECTION VIII — EFFECT OF CHEMICAL AGENTS UPON 
PROTOPLASMIC ACTIVITY 

All development, all differentiation, and all functional activity 
of living organisms are the result of protoplasmic activity ; but 
protoplasmic activity is, in the last analysis, chemical activity, 
and it is certainly subject to many of the laws controlling ordi- 
nary chemical reactions. It is noticeable in the study of vital 

1 Weisniann, Germ Plasm, pp. 399-400. 

2 The writer has somewhere read that animals on shipboard become rapidly 
lighter in color as the coat becomes exposed to intense cold, but he is unable to 
verify the report. 



EXTERNAL INFLUENCES AS CAUSES OF VARLATION 265 

processes from the chemical standpoint that some substances 
exert no influence upon protoplasm, while others kill it out- 
right; that some accelerate and others retard its normal action; 
and that some suspend activities more or less completely, while 
others divert them into entirely 7iezu cJiannels. Here is varia- 
tion due to chemical disturbance of the material basis of life, 
and it is well to study somewhat in detail this " modification of 
vital actions " from chemical causes.^ In studying this class of 
phenomena it is necessary, of course, to make use of simple 
organisms of one or of few cells, and while we cannot reason 
directly from these to the higher animals and plants, still all 
evidence goes to show that the differences are not so much in 
kind as in complexity. 

Oxygen. All experiments indicate that no protoplasm can 
long survive in the absence of oxygen. In most cases it is taken 
directly from the air, but in others, as in anaerobic bacteria, it 
is probably extracted from surrounding compounds containing 
oxygen. Diminished oxygen retards and increased oxygen and 
ozone greatly accelerate the vital processes, ^ all zuitJiout cJiang- 
ing their character. 

A number of oxygen-containing substances greatly retard or 
even destroy vital activities, probably through " oxidation of the 
protoplasm." ^ If this be the case, and the material basis of 
life is subject to the ordinary chemical process of oxidation, it 
shows that vital processes in the last analysis rest upon a strong 
chemical basis. 

Hydrogen peroxide (H^Og), only slightly different from water 
(H2O), is a powerful oxidizing agent. One part in ten thousand 
(0.0 1 per cent) in hay infusion killed all ciliata in from fifteen to 
thirty minutes. Algae survived a o. i per cent solution but ten 
or twelve hours, and died in a 10 per cent solution in a few 
minutes. *' Salts of chromic, manganic, permanganic, and hypo- 
chlorous acids act as intense poisons, apparently by directly yield- 
ing oxygen atoms to the plasma proteins." Chlorin, iodin, and 

^ C. B. Davenport, Experimental Morphology, Part I, chap, i, from which the 
data in this section are largely taken. 

2 Small animals confined in an atmosphere of pure oxygen exhibit greatly 
increased activity and " live themselves to death " in a few hours. 

^ C. B. Davenport, Experimental Morphology, Part I, p. 3. 



266 CAUSES OF VARIATION 

bromin in the presence of water act " fatally upon all organisms 
by splitting [the] water, forming hydro-halogen compounds, and 
leaving the oxygen to unite with the living protoplasm." ^ 

Hydrogen. Amoebae subjected to an atmosphere of hydrogen 
for twenty-four minutes became motionless, some having assumed 
the spherical form. The same general result followed in trades- 
cantia hairs, but from the fact that normal activity was restored 
by admitting air it was assumed that the results arose not from 
any injurious effect of hydrogen but from the exclusion of oxygen.^ 

Oxids of carbon, — CO2 and CO. These two oxids of carbon 
have very different effects upon protoplasm. The former, like 
hydrogen, seems to act only by excluding oxygen, death, when 
it results, being due mainly to asphyxia, while the latter kills by 
attacking the protoplasm directly.'^ 

Catalytic poisons.* A large number of unstable carbon com- 
pounds, neither acid nor basic and therefore not characterized 
by intense chemical action, are yet violent poisons. Here belong 
the anaesthetics, as chloroform, chloral, ethyl, ether, alcohols, etc. 

These unstable compounds are characterized by a " lively 
condition of molecular movement " (Nageli), which is considered 
to disturb the normal movements of the protoplasm, or " to 
lead to chemical transformations in the unstable albumen of the 
protoplasm" (Loew). 

Catalytic substances are supposed to exert their action not by 
entering into and effecting new combinations but by disturbing, 
through their mere presence, the usual behavior of bodies. It 
is in this way that protoplasm suffers in their presence. Thus 
hydrochloric and prussic acids unite only at high temperatures, 
except in the presence of various ethers, when they will unite 
even at — 15°. The vigor of this catalytic action is in proportion 
to the molecular composition.^ Thus in the methan series with 
CHg as the base we have CH^, C2Hg, CgHg, etc., in which 

1 C. B. Davenport, Experimental Morphology, Part I, p. 4. 

2 Ibid. p. 5. 

3 Ibid. p. 6. 

^ A free extract from C. B. Davenport, Experimental Morphology, Part I, 
pp. 7' 8. 

^ The facts here stated are taken almost literally from C. B. Davenport, 
Experimental Morphology, Part I, pp. 7-8. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 267 

" the poisonous action increases up to a certain limit in proportion 
to the number of C atoms," while "above this hmit the com- 
pounds are more stable and are more indifferent, as for example 
paraffin {C^^H^^ to €271^53)." 

Again, in such a series, if the H atoms become replaced by 
one of the halogens, the poisonous properties correspondingly 
increase ; thus : ^ 

CH4, marsh gas, innocuous. 

CH3CI, slightly anaesthetic. 

CHCI3, chloroform, powerful anaesthetic. 

CCI4, very dangerous, stupefying involuntary muscles. 

Chloroform and ether affect all protoplasm, both plant and 
animal, higher as well as lower. They seem to produce at first 
(two to five minutes in a 25 per cent water solution) a "very 
intense excitement in the movement of the protoplasm," fol- 
lowed by "strong vacuolization, and then the cytoplasm grad- 
ually becomes immobile " and dies, if the influence is continued. 
In a similar way the various alcohols exert stupefying effects in 
proportion to the number of CH2 radicals present, and carbon 
disulphid (CSg) is one of the most powerful catalytic poisons. 

Protoplasm is therefore subject to catalytic disturbances, in 
which it is not different from other and more ordinary chemical 
materials, — a fact in itself exceedingly significant to the stu- 
dent looking for fundamental causes of variation. 

Poisons which form salts."-^ These are acids and bases which 
Loew believes, as stated by Davenport, " unite [directly] with 
the protein substances of the protoplasm, producing salts," — 
disturbances that of course soon lead to death. Thus " formic 
acid, even in small per cents, — 0.05 per cent to 0.006 per cent, 
— prevents the development of bacteria. On the other hand, 
some protoplasm has acquired a resistance to organic acids, the 
vinegar eel Uving in 4 per cent acetic acid," and the gland cells 
of some marine Gastropoda secrete from 2 per cent to 3 per 
cent of H2SO4, a strength which is fatal to most protoplasm. 

1 The halogens — fluorin, chlorin, bromin, and iodin — form a group of sub- 
stances of very similar chemical properties, but form, in the order named, a 
decreasing series as to chemical energy. 

■•^ C. B. Davenport, E.xperimental Morphology, Part I, pp. 12-14. 



268 CAUSES OF VARIATION 

Nageli's experiments ^ indicate that water distilled in cop- 
per vessels, or standing four days in other vessels with twelve 
clean copper coins per each liter of water, was fatal to Spiro- 
gyra, though the proportion of copper to water was but i to 
77,000,000. 

These reactions, resulting in death rather than in modified 
action, are important, not as showing primary causes of varia- 
bility but as proving again that living protoplasm is still subject 
to many of the chemical affinities that controlled its elements 
before they became organized into living matter. It must be 
remembered in this connection that many of these substances 
attack only living protoplasm, having no action upon dead pro- 
toplasm, showing that at death the highly complex materials 
have, to some extent at least, broken down. 

The action of some poisons, like nicotin, is proportional to 
the "differentiation of nervous substance" ; others, like cocain 
and atropin, first excite and then paralyze the central nervous 
system of vertebrates, but act as violent poisons upon undiffer- 
entiated protoplasm (Protozoa).^ 

Toxic poisons. It is not the germ that kills, but rather its 
specific toxin that deranges some of the vital functions beyond 
endurance. The dire effects of germ diseases are therefore due 
not so much to the organisms themselves as to their constant 
manufacture within the body of a chemical poison which the 
protoplasm cannot endure and preserve its normal functions. It 
may die in the attempt, or it may succeed and become accli- 
mated, but while the struggle is on, the body functions will be 
considerably disturbed. It is significant that compounds similar 
to those of disease-producing bacteria have been " extracted from 
the seeds of some phanerogams ; for example, ricin from the seeds 
of the castor-oil bean, etc." In this class may come the poisons 
secreted by certain animals, as the rattlesnake and cobra, fatal 
to vertebrates but innocuous to Infusoria and Flagellata. 

It is also noteworthy that the blood serum of one species 
rapidly dissolves the corpuscles of another (red and white), and 
is therefore injurious or fatal according to the amounts present.^ 

1 C. B. Davenport, Experimental Morphology, Part I, p. 14. 

2 Ibid. pp. 23 and 24. ^ Ibid. p. 22. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 269 

Specific secretions and glandular activity. The fact just men- 
tioned introduces a subject full of interest. It appears that each 
species, and perhaps each individual, is engaged in the produc- 
tion of chemical substances (whether the result of metabolic or 
katabolic activity is uncertain) which exert specific action upon 
living matter. 

It is significant that some of the lower organisms producing 
definite substances die from the injurious effects of their own 
product,^ unless this is removed as formed, and that higher ani- 
mals are supplied with elaborate excreting apparatus, strongly 
suggesting that certain of their products are deleterious to the 
organisms that produced them, while in other cases they are 
clearly beneficial. In this connection Loeb remarks : ^ 

It is perhaps not impossible that those mental diseases that are heredi- 
tary are, in reality, chemical diseases caused by poisons that are formed 
in the body, just as special substances — for instance, alcohol, hashish, 
and other intoxicating substances — produce temporary mental diseases. 
The delirium of fever, as well as certain other mental diseases, may owe 
their origin to poisons which are formed in the body. It is quite possible 
that these poisons are also formed in the normal body. It is only necessary 
that they be formed in somewhat larger quantities or destroyed in some- 
what smaller quantities in the body of the insane than in the normal man.'^ 

It is further not at all necessary that the hypothetical poisons which 
cause mental diseases be formed in the central nervous system. They may 
be formed in any organ of the body. It is only necessary that they affect 
the central nervous system ; in other words, that they be nerve poisons. 

Nothing is better qualified to make this view clear than the result which 
the destruction of the thyroid gland has on the mental and physical devel- 
opment of children. We know that in case of degeneration of the thyroid 
gland the growth and mental development of the child are retarded. Idiocy 
may result from the destruction of the thyroid gland. It has been found 
that an improvement, or even a cure, can be attained by feeding patients 
afflicted with this trouble with the thyroid substance of animals.'' Baumann 
found that the thyroid gland contains an element which is contained in no 
other organ of the body, — namely, iodin. 

1 The yeast plant that forms alcohol dies when the solution has reached a 
strength of about 20 per cent. 

2 Loeb, Physiology of the Brain, p. 207. 

^ It is said by Lombroso, and others agree, that the criminal is characterized 
by excessive amounts of urea. 

* Medicinal preparations from various glands are now regularly supplied by 
the large slaughterhouses. 



2 70 CAUSES OF VARIATION 

Insect poisons. The poison of bees — formic acid — is fatal 
to insects and small animals, and in sufficient quantity to the 
larger vertebrates, including man, though frequent stings of a 
moderate number lead rapidly to acclimatization. It is note- 
worthy, too, in this connection that the sting of the insect 
(mud wasp, for example) does not always kill but often merely 
paralyzes, so that the creature stored with the egg will remain 
alive to furnish food to the larvae some weeks later. 

Galls. Galls are the direct result of the sting of an insect, 
leaving a specific poison to act upon a particular form of proto- 
plasm. The result is not death but a diverting of the activities 
into entirely new channels. Darwin states that " no less than 
fifty-eight kinds of gall are produced on the several species of 
oaks by Cynips with its sub-genera, and Mr. B. D. Walsh states 
that he can add many more." ^ 

Darwin further remarks that many gall insects are exceedingly 
small, and that consequently the drop of poison they inject must 
be exceedingly minute ; moreover, it is never injected but once. 
The growth that follows, however, is specific and continuous. 
He quotes Walsh as saying, " Galls afford good, constant, and 
definite characters, each kind keeping as true to form as does 
any independent organic being," ^ and he calls our attention to 
the fact that seven of the ten distinctly different galls produced 
on the willow are by insects which, " though essentially distinct 
species, yet resemble one another so closely that in almost all 
cases it is difificult and in most cases impossible to distinguish 
the full-grown insects one from another." The difference in the 
quality of the poison secreted by insects so nearly alike cannot be 
great, yet it is sufificient to give rise to galls widely different. 
Last, and not least, he mentions that " Cynips fccjmdatrix has 
been known to produce in the Turkish oak, to which it is not 
properly attached, exactly the same kind of gall as on the 
European oak. These latter facts apparently prove that the 
nature of the poison is a more poxvcrful agent in determining 
the form of the gall than [z>] the specific character of the tree 
ivhich is acted on." ^ 

1 Darwin, Animals and Plants, II, 272. ^ ibid. p. 273. 

^ Ibid, (second edition), 273. Tlie italics are mine. 



EXTERNAL INFLUENCES AS CAUSES OF VARLVFION 271 

Tumors. Those overgrowths of various parts of the body, 
called tumors, arising from causes not well understood, have 
their specific characters as truly as if derived from inherit- 
ance. Whether the character of the tumor is derived primarily 
from the tissues affected or from some outside specific cause is 
not known, but it is a significant fact that the protoplasm, ivhich 
derived its cJiaracters originally by inheritance , has undergone 
permanent and definite alteration tJirongJi the operation of causes 
absolutely distinct from inheritance , whether internal or external 
to the organism, thus sJiowing the possibility of diverting the ener- 
gies of inJierited 7fiaterial into absolutely new channels through 
apparently slight causes. 

At this point it is well to call our attention to the profound 
changes (permanent variations) wrought upon the constitution 
of the individual by such internal-external circumstances as vacci- 
nation or the injection of antitoxin, as well as to the immunity 
acquired through a single attack of an infectious disease. 

Germination of seeds. It is a well-known fact that certain 
chemicals accelerate and others retard the process of germina- 
tion. Just why this is true is not clear on any other ground 
than that of the ordinary susceptibility of growing protoplasm 
to stimulants and sedatives. The process of germ development 
requires, in addition to what is contained within the seed, only 
oxygen, water, and a favorable temperature ; the influence of 
other chemicals must be indirect. 

Chemotaxis and chemotropism.^ The influence of chemical 
substances upon the locomotion of free-moving organisms is tech- 
nically known as chemotaxis, and their influence upon the direc- 
tion of growth (in plants) is known as chemotropism.'^ The 
distinction is hardly worth observing for our purposes, because 
both phenomena arise from a direct influence of chemical sub- 
stances upon living protoplasm, either attractive or repellent. If 
. attractive, it (the protoplasm) will move toward the material in 

1 C. B. Davenport, Expeiimental Morphology, Part I, 32-45; Part II, pp. 
335-342; Loeb, Physiology of the Brain, pp. 50, S8-90, iiS, 1S6-188. 

2 As has already been noted, the same distinction is often observed between 
geotaxis, the influence of gravity upon locomotion, and geotropism, its influence 
upon the direction of growth ; also between heliotaxis and heliotropism as cover- 
ing corresponding influences of the sun (light). 



2 72 CAUSES OF VARIATION 

question, providing it is free to do so (as in the case of the 
lower plants and all animals), or its growth will be directed 
toward it if (as in the case of higher plants) it is fixed and un- 
able to move. The former is, strictly speaking, chemotaxis ; the 
latter is chemotropism. For our purposes it is a distinction 
without a difference, because in the latter case the plant is 
unable to indulge in locomotion, and performs the hearest pos- 
sible act in changing the direction of growth. Both are loco- 
motion under the circumstances ; both are due to the same 
cause, — a chemical affinity or attraction, — and they differ 
because of differences in the organisms affected in respect to 
the power of locomotion, not because of differences in the nature 
of the forces in action. The two terms are, therefore, for our 
purposes, synonymous as denoting a power of attraction between 
protoplasm and certain ordinary chemical compounds such as to 
cause the protoplasm to approach if it be free to move, or, if not, 
to grow in that direction, — which is all that can be done under 
the circumstances to satisfy the affinity. 

Chemotaxis, or chemotropism as the writer prefers to call 
it,^ has but a slender hold upon higher animals. It appears to 
be localized in the nostrils and to manifest itself only in the 
sense of smell, agreeable or otherwise ; but in lower organisms, 
even in many insects, it is apparently not confined to a minute 
fraction of the surface, but pervades the whole organism with 
an influence that is all but overpowering. It may of course be 
aided or opposed by other tropisms, as gravity or light, in which 
case the total result is the algebraic sum of all the energies 
operative, but that chemotropism is a force to be reckoned with 
in development is a fact not to be doubted. 

Examples of chemotropism. ^ Englemann noticed that bac- 
teria under a cover glass will gather along the margin, or if 
green algae be introduced they will cluster about them so long 
as they are producing oxygen, but in the darkness they will not 

1 The ending " taxis " is from the Greek, meaning assortment or arrangement ; 
the ending " tropism" is from " tropic," to turn. " Chemotropism " is pronounced 
ke-mot'rd-pTzm. 

■^ Until otherwise noted what follows is a free though not exact transcript from 
data given in C. B. Davenport's Experimental Morphology, Part I, pp. 32-39. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 273 

be affected. In the same way nearly all kinds of motile organ- 
isms are now known to be influenced by a variety of chemical 
substances. 

Lubbock has shown that ants retreat from essence of clove, 
lavender water, etc.,^ placed within one fourth inch of their 
path, and Loeb found that the larvae of flies creep towards a 
piece of fiesh brought nearer than 1.5 cm. Not only flesh and 
decaying meat, but meat juice in a glass, will allure, while fat 
has no effect. Every farmer knows how quickly flies are 
attracted by a dressed animal, and carrion birds by a carcass. 

According to Pfeffer's experiments the inorganic salts of 
potassium, sodium, calcium, ammonium, magnesium, and many 
other metals in 0.5 per cent solution act attractively upon Bac- 
terium termo. " Inorganic acids ... in general act repulsively," 
but phosphoric acid and the phosphates are strongly attractive. 
Dewitz states that mammalian spermatozoa are attracted by 
KOH. 

" Alcohol in grades between 10 per cent and i per cent acts 
repulsively towards bacteria," but "glycerin is neutral." Malic 
acid, which is of wide distribution among plants, is strongly 
attractive to spermatozoids, even in a 0.00 1 per cent solution, — 
a fact which is highly significant. 

This principle of chemotropism acting on higher organisms 
gives rise to characteristic movements. In Loeb's experiments 
on actinians ^ a piece of meat laid upon the tentacles so affected 
them as to cause a bending which carried the meat into the 
mouth, while a wad of water-soaked paper had no effect, but lay 
there until removed. If, however, the paper was soaked in meat 
juice it was received the same as a piece of real meat. (See 
Fig. 29.) 

Now the actinian, consisting simply of a sac with a row of 
tentacles around the edge, without brain or nerve centers of 

1 Experimenting upon means of preventing the ravages of tlie corn-root aphis, 
Forbes of Illinois found that a small amount of oil of lemon on the seed corn, 
before planting (costing but ten cents per acre), is able by its strong odor to 
repel ants from the neighborhood of the corn hill for no less than six weeks 
after planting. As the young aphis is absolutely dependent upon the attentions 
of the ant, this treatment is effective. 

2 Loeb, Physiology of the Brain, pp. 49-50. 



274 



CAUSES OF VARIATION 



any kind, is certainly incapable of exercising anything like in- 
telligent choice. The characteristic movement must have been 
due to the specific chemical action of the juices of the meat 
upon the protoplasm of the muscle fibers of the tentacle, while 
the paper had no such action and hence no movement followed. 
This movement and non-movement look like intelligence or 

instinct and have often 
passed for one or the 
other to the infinite con- 
fusion of the subject.^ 

^' Lnmbrici foetidi live 
in the decaying compost 
of old stables, and prob- 
ably the chemical nature 
of certain sub- 
stances con- 
tained in the 
compost holds 
them there," 
for "when one 
half of the 
bottom of the 
box is covered 




Fig. 29. Stimulating effect of certain chemicals upon mus- 
cular action : a piece of meat laid upon the tentacles of 
the actinian stimulates their action and it is drawn into the 
mouth. A piece of paper similarly placed is inoperative 



with moist blotting paper and the other half with a thin layer 
of compost, all the worms will gather on the compost side." 
Decapitated worms behave in the same way,^ so that the 
effect is due to a general influence, not to " nerve centers." 
Loeb says,'^ " I have often placed pieces of lean meat and 
pieces of fat from the same animal side by side on the window 
sill, but the fly never failed to lay its eggs on the meat and not 
on the fat." (He tried, of course without success, to raise larvae 
in the fat.) " It can easily be shown that larvae of the fly are posi- 
tively chemotropic towards certain chemical substances which 
are formed, for instance, in decaying meat or cheese, but which 
are not formed in fat. The substances in question are probably 
volatile nitrogenous compounds," and "the chemical effects of 

1 This subject will be pursued further under " Instinct and Reflex Action." 

2 Loeb, Physiology of the Brain, p. 90. ^ Ibid. pp. 186-187. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 275 

the diffusing molecules on certain elements of the skin influence 
the tension of the muscles," causing motion. 

The female fly is attracted by meat, the same as are larvce, and 
" as soon as the fly is seated on the meat chemical stimuli seem 
to throw into activity the muscles of the sexual organs, and 
eggs are deposited on the meat." This chemical stimulus is 
about all there is of the wonderful "instinct" by which insects 
are led " always to deposit their eggs in exactly the right places." 

These and similar examples show the effect of certain chem- 
icals upon free-moving organisms. It remains to illustrate their 
effect upon the direction of grozutJi among plants, which are not 
free to move. 

First of all, we are to note the effect of certain chemicals upon 
the tentacles of insectivorous plants. Darwin noticed that "when 
drops of water or solutions of non-nitrogenous compounds are 
placed upon the leaves of the sundew, Drosera, the tentacles 
remain uninflected ; but when a drop of a nitrogenous fluid, such 
as milk, wine, albumen, infusion of raw meat, saliva, or isinglass 
is placed on the leaf, the tentacles quickly bend inwards over 
the drop."^ Darwin found that of " nine salts of ammonia tried, 
all caused inflection, and of these the phosphate was the most 
powerful," and that " sodium salts in general caused inflection 
with extreme quickness." This action of nitrogenous, phos- 
phatic, and other chemicals common to animal life, was the 
same upon the tentacles of insectivorous plants as upon' the 
tentacles of lower animals subsisting upon the same kind of 
food.^ Thus plant and animal tissues appear to be subject to 
the same general laws in this regard. 

From this point of departure, common to both plant and ani- 
mal, we note that the animal, free to move, does so in response 
to this class of stimuli. What does the plant do that cannot 
move, even as tentacles move .-* In other words, how does chemot- 
ropism affect the direction of grozvth among higher plants ? 

Roots in general are supposed to grow toward oxygen, and 
pollen tubes will certainly turn toward the stigma of the flower, 

1 C. B. Davenport, Experimental Morphology, pp. 335-336. 
- See the e.xperiment on actinians previously quoted from Loeb, Physiology of 
the Brain, pp. 49-50. 



276 CAUSES OF VARIATION 

the supposition being that sugar is the special attracting sub- 
stance in the latter case. It is noteworthy that the pollen tube 
is attracted not simply to its own stigma but also to the pistil 
and the ovule of other species, even of a different genus with 
which it is unable to unite. ^ Davenport says :^ 

The results of experimentation upon chemotropism show that various 
substances may direct the growth of such elongated organs as tendrils, roots, 
and hyphae of plants. ... In many instances it can be shown that the 
direction of growth is on the whole advantageous to the organi.sm. ... In 
other cases, however, the response seems to have no relation to adaptation. 

The immediate cause of change of direction is "excessive 
growth on one side, due to excessive imbibition or to excessive 
or restricted assimilative activity." 

The evidence seems conclusive that the chemical elements 
constituting living matter have not entirely lost their ordinary 
affinities and properties ; that protoplasm is in many respects 
subject to the laws of other chemical compounds ; that its activ- 
ities may be accelerated or retarded ; that they may be tempo- 
rarily or even permanently modified in character by chemical 
alteration, or even entirely destroyed by entering into new and 
strange combinations with surrounding substances. Here is a 
real cause, at least of occasional variation, — possibly of those 
sudden changes we call mutation. 

Rhythmical contraction of muscle instituted by certain chem- 
ical substances. The irritability and consequent contraction of 
muscles due to influences of a chemical nature have already been 
noticed, as in the case of the movement of the tentacles of the 
actinian, the attractive or repulsive effect of certain odors, and, 
to some extent, in the placing of insect eggs in "exactly the 
right spot." 

It is now well known that certain salts exert a specific action 
upon muscle, exciting even rhythmic contraction. As long ago 
as 1 88 1 Biedermann discovered that if the muscle of a frog be 
carefully excised at a low temperature {o°-io° C), then weighted 
and dipped into a 0.6 per cent solution of sodium chlorid con- 
taining also small amounts of sodium phosphate and sodium 

1 C. B. Davenport, Experimental Morphology, p. 339. ^ Ibid. p. 343. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 277 

carbonate "one observes as a rule, after a longer or shorter period 
of rest, that the immersed muscle begins to beat rliytJimically.'" 

On this point Loeb remarks that sometimes only a mere 
tremor is noticeable, at others violent contractions ; that some- 
times only individual fibers are active, at others the whole muscle 
is involved ; and that " at low temperatures these phenomena 
may continue for days." ^ 

These facts, together with Ringer's and Howell's statements 
that calcium and potassium salts exert a direct action upon the 
heart, led Loeb to extend the Biedermann investigations. He 
subjected the gastrocnemius muscle of a frog (unweighted) to a 
series of solutions of chemically pure materials in twice-distilled 
water.2 

These experiments not only confirmed Biedermann's findings 
that the salts of sodium were able to excite rhythmic muscular 
contraction but they also added lithium, caesium, and rubidium 
to the list of bases, and the salts of bromin, iodin, and iron to 
those of carbon, chlorin, and phosphorus. These movements 
are periodic and continue into the second day, even at room 
temperatures. 

Loeb determined that if a muscle be immersed in a 0.7 per cent 
solution of sodium chlorid, contractions will begin in from sixty 
to ninety minutes, but that " if a trace of alkali is added, con- 
tractions begin much sooner." This acceleration he attributes 
to the hydroxyl (OH) in the alkali added. Not only that, but he 
ascribes the effect to the H involved in the hydroxyl, because 
the same action follows the addition even of inorganic acids, as 
HNO3, " if the same number of hydrogen ions are contained 
in the unit volume";^ but Loeb hastens to assure us that 
neither the hydrogen ions nor the hydroxyl ions " belong to 
those which are capable of Hberating rhythmic contractions." 
They only accelerate the action of those which of themselves 
possess this power. 

The action of sodium and other chemicals in exciting contrac- 
tion is, in the opinion of Loeb, to be ascribed to their entering 

1 Loeb, Studies in General Physiology, Part II, p. 518. 

2 Ibid. pp. 519-538. 

3 Ibid. p. 527. 



278 CAUSES OF VARIATION 

the muscle and there forming with its substance definite com- 
pounds, and he beheves the accelerating effect of H or OH is 
due to their catalytic action in facilitating the formation of these 
compounds. In this connection it is to be remembered that the 
serum of the body which bathes the muscles is always, in health, 
strongly saline and slightly alkaline. 

Further experiments clearly showed that the salts of potas- 
sium and those of calcium, magnesium, strontium, manganese, 
and cobalt tend strongly \o prevent contraction, this being espe- 
cially true in the case of potassium and calcium, forcing the 
conclusion that certain definite substances are necessary to con- 
traction ; that certain others tend to accelerate and still others to 
retard this characteristic activity of in?iscular tissue. 

Artificial parthenogenesis through changes in the surrounding 
solution.^ The indefatigable labors of Jacques Loeb upon this 
subject have not only thrown much light upon the essential 
features of fecundation, but incidentally they have afforded 
results of high value in determining the nature and range of 
external influences upon the characteristic activities of living 
matter.- 

It had long been known that many of the eggs of sea 
urchins, arthropods, and marine worms, even zvhen unfertilized, 
would, if left for a comparatively long time in sea water, begin 
to segment, reaching the two- and sometimes the four-celled 
stage. Loeb, and later Morgan, found "that if the concentra- 
tion of the sea water be raised sufficiently by the addition of 
certain salts, a segmentation of the nucleus takes place with- 
out any segmentation of protoplasm [cytoplasm]. Such eggs, 
however, when brought back into normal sea water divide into 
as many cells as there were preformed nuclei." '^ In none of 
these experiments did the cell division "lead to the formation 
of a blastula. A heap of cells, at the best about sixty, were 
formed, and then everything stopped." As in the case of tumors 

1 Loeb, Studies in General Physiology, Part II, pp. 539-691. 

2 These investigations have been published from time to time, especially in the 
American Journal of Physiology, and later (1905) in book form under the title, 
Studies in General Physiology. 

^ Loeb, Studies in General Physiology, Part II, pp. 540-541. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 279 

and galls, here was growth without systematic differentiation ; 
cell division without the formation of an embryo. 

Encouraged by this degree of segmentation and by his experi- 
ments upon irritability of muscle, Loeb tried a great variety of 
solutions, in various degrees of concentration, in the hope of 
carrying the segmentation far enough to produce real embryos 
and live, free-moving larvae. 

He was greatly hampered by the fact that unfertilized eggs 
do not form membranes as do fertilized, so that growth tended 
to be formless, and even when assuming definite form in the 
blastula^ stage there were often formless masses of dividing 
matter lying to one side. 

Briefly stated, the following facts developed during the prog- 
ress of this systematic experiment : 

1. In a solution of sodium chlorid the eggs were unable to 
reach even the blastula stage. 

2. With the addition of MgClg, however, blastulas were formed, 
but they did not move. When afterward placed in normal sea 
water movement soon appeared. 

3. With three chlorids (Na, K, and Ca) "the eggs not only 
reached the blastula stage and swam around in the most lively 
way, but they reached the gastrula and even the pluteus stage, 
with the exception, however, that practically no skeleton was 
formed." - Such larvae lived about ten days. 

4. The addition of a trace of Na2C03 resulted in the formation 
of a skeleton, but it was not quite normal. It was made normal 
by adding a trace of MgClg. 

1 Three early stages are characteristic of the early development of all embryos : 
(i) the morula, or " mulberry " stage, in which cell division gives rise to a globular 
mass of rounded cells, each more or less distinct, like the grapes on a bunch or 
the seeds of a mulberry; (2) the blastula stage, in which the outer cells become 
condensed, showing a distinct outer layer, — the blastoderm ; and (3) the gastrula 
stage, in which one side becomes pushed in (invaginated), as one would push in a 
hollow rubber ball with his thumb, forming a kind of mouth and stomach. A few 
forms never get beyond this stage, but most pass quickly through it, differentia- 
tion proceeding rapidly. In higher animals the outer layer (ectoderm) gives rise 
to the skin and its appendages, the inner (endoderm) to the internal organs. 
Among sea urchins, which were here under experiment, the next stage is known 
as Xhe pluteus, — the stage of free-moving larvae. It was this stage the experi- 
menter desired to produce. 

2 Loeb, Studies in General Physiology, Part II, pp. 585-5S6. 



28o CAUSES OF VARIATION 

5. All experiments indicated that it is impossible to secure 
more than the beginning of segmentation from an unfertilized 
egg without raising the co7icentration of the sea water. 

6. But for this purpose MgCl2 was peculiarly effective and 
normal plutei (free-swimming larvae) developed from unfertilized 
eggs lying in normal sea water after having lain for two hours 
in a solution of MgCl2 of proper strength. ^ 

7. These effects seemed to be due to the increased concen- 
tration in the sea water, bringing about increased osmotic pres- 
sure and resulting in a loss of water on the part of the egg. 
This loss of water seems to be the active cause of rapid seg- 
mentation, and a variety of substances were discovered which 
were able to bring it about. 

8. The principal difference noticeable in the plutei was that 
those developed from fertilized eggs swam freely at the top of 
the water, while those developed from unfertilized eggs " were 
all at the bottom of the dish and unable to rise." 

9. Experiments upon the marine annelid Chaetopterus^ indi- 
cated that artificial development is easier than with the sea 
urchin, but that it is achieved by a different solution. In the 
words of the experimenter, " We may say that Chsetopterus 
possesses a higher degree of parthenogenetic tendency than the 
Arbacia [sea urchin] eggs," ^ and "if the sea water contained 
only a slightly greater proportion of K, we should find that 
Chaetopterus was normally parthenogenetic." * 

10. If certain forms are prevented from becoming partheno- 
genetic by the constitution of the sea water, we may infer that 
those which are naturally parthenogenetic are so by the consti- 
tution of the blood or the sea water enabling the egg to develop.^ 

11. "The bridge between the phenomena of natural and 
artificial parthenogenesis is formed by those animals in which 

1 Loeb, Studies in General Physiology, Part II, p. 624. 

2 " Mead had already found that if 0.5 per cent KCl is added to sea water the 
unfertilized eggs of Chaetopterus throw out their polar bodies, while the addition 
of 0.5 per cent NaCl produced no such effect." — Loeb, Studies in General 
Physiology, Part II, pp. 656-657. 

^ Loeb, Studies in General Physiology, Part II, pp. 654-655. 

4 Ibid. p. 665. 

5 Ibid. p. 683. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 28 1 

physical factors decide whether or not their eggs develop par- 
thenogenetically." ^ The consideration seems to be largely one 
of change in osmotic pressure, some organisms requiring increase 
and some decrease. Plant lice are parthenogenetic only at high 
temperatures and when the host plant has plenty of water. " If 
we lower the temperature or let the plant dry out, sexual repro- 
duction occurs." ^ It seems to be decided that Artcinia salina 
living in brackish waters is parthenogenetic, while its nearest 
fresh-water relative, Branchipus, is not.^ 

12. From the fact that the beginning of segmentation is com- 
mon in unfertilized and untreated eggs of many forms, it seems 
to follow that the effect of fertilization or of treatment is largely 
to accelerate a process which is able to begin alone but which 
proceeds so slowly as to be overtaken by destructive processes 
and the death of the Q.^g before an embryo can form. 

13. The introduction of a small amount of a catalytic sub- 
stance at the critically proper time (at maturity) seems in most 
cases necessary to a cell division sufficiently rapid to insure the 
continuation of life. 

14. The function of the spermatozoon would seem therefore 
to be twofold, — first, to introduce such a catalytic substance, 
and second, to convey hereditary material. 

No student can consider these fundamental matters and fail 
to realize . the profound effect of external influences upon in- 
ternal activities, nor can he avoid the conclusion that we must 
revise our ideas as to the relation even of inorganic chemistry 
and physical forces to the processes of life. Much that we 
have considered as morphological and peculiarly vital is, after 
all, evidently due to the operations of ordinary chemical and 
physical laws. This does not make the facts of variability 
less significant, but it does show the extent to which living 
organisms have become accustomed to their ordinary sur- 
roundings. 

^ Loeb, Studies in General Physiology, Part II, p. 683. 

2 " Janosik has found segmentation in the unfertilized eggs of mammalians." 
— Loeb, Studies in General Physiology, Part II, p. 543. Loeb expresses the con- 
viction that possibly " only the ions of the blood prevent the parthenogenetic 
origin of embryos in mammalians," and that a change in their blood might be 
followed by parthenogenetic development. 



282 CAUSES OF VARIATION 

SECTION IX — EFFECT OF SALINE SOLUTION UPON 
DEVELOPMENT IN AQUATIC ANIMALS 

Sea water differs from fresh water in two particulars, salinity 
and density, both of which exert marked influence upon animal 
life and between which it is often difficult to discriminate. A 
goldfish plunged into sea water at first shows " violent incoor- 
dinated movements," but shortly " becomes immobile and rises 
to the surface by virtue of its lower specific gravity." ^ 

" The effect of fresh water upon marine organisms is equally 
striking. They go immediately to the bottom and move with 
difficulty. Swimming animals swim badly if at all, and small 
fishes have to make much exertion to rise to the surface." ^ 

On many marine animals, as mollusks and fish, fresh water 
acts as an anaesthetic, the mollusks soon yielding to paralysis, 
the fish appearing to suffer from lack of air. "The respiratory 
movements become deep and rapid. . . . The tissues become 
swollen so that soft-bodied animals are visibly deformed, — in 
fishes the eyes are forced out, the foot of gastropods swells, the 
blood corpuscles swell up and burst, and muscular tissue may 
increase as much as six times in volume." ^ 

Many of these effects are clearly due to differences in pres- 
sure which may amount to many atmospheres, but it remains 
to separate, so far as may be, the effects of salinity from those 
of specific gravity. 

Rather startling claims have been made from time to time 
as to the conversion of one species into another by altering the 
degree of salinity. Further investigation seems to show that in 
all such cases intermediate forms are known to occur, which 
argues that the two forms which had been recognized as dis- 
tinct were not both good species ; that is to say, it is a case of 
one species with wide variability as to certain characters, not that 
of two distinct and well-defined species. If, however, differences 
in salinity are effective in bringing about alterations in even a 
single character, the fact is of interest here, no matter what 
specific lines should be drawn by the biologist. 

1 C. B. Davenport, Experimental Morphology, Part I, p. 79. 

2 Ibid. pp. 79, 80. 



EXTERNAL INFLUENCES AS CAUSES OF VARLVITON 283 

The small crustaceans Artcmia salina and A. viilhausaiii 
have been recognized as distinct, the former living in brackish 
and the latter in still more concentrated waters, the two differ- 
ing mainly in the number and length of bristles borne at the 
extremity of the caudal fins. 

Early in the seventies Schmankewitsch published an account 
of the mutual conversion of each form into the other, but the 
facts as given by him have been greatly overstated, as frequently 
happens in repetition. They are sufficiently significant as first 
reported, and it seems well to give the original statement as 
recorded by Bateson,^ which is as follows : 

The salt lagoon, Kuyalnik, was divided by a dam into an upper and a 
lower part ; the waters in the latter being saturated with salt, while the 
waters of the upper part were less salt. By a spring flood in the year 1871 
the waters of the upper part of the lake swept over the dam and reduced 
the density of the lower waters to 8° Baume (= about sp. g. 1.051), and 
in this water great numbers of A. salina then appeared, presumably having 
been washed in from the upper part of the lake or from the neighboring 
salt pools. After this the dam was made good and the waters of the lower 
lake, by evaporation, became more and more concentrated, being, in the 
summer of 1872, 14° B (about sp. g. 1.103); in 1873, 18° B (about sp. g. 
1.135) ; in August, 1874, 23.5° B (about sp. g. 1.177), and later in that year 
the salt began to crystallize out. In 187 1 the Artemia [as first carried 
over] had caudal fins of good size, bearing eight to twelve, rarely fifteen 
bristles, but with the progressive concentration of the water the genera- 
tions of Artemia progressively degenerated, until at the end of the summer 
of 1874 a large part of them had no caudal fins, thus presenting the 
character of A. milharisenii. — Fischer and Milxe-Edwards. 

Bateson adds : 

A similar series was produced experimentally by gradual concentration 
of water, leading to the extreme form resembling A. iiiilhauseiiii. It was 
found also that if the animals without caudal fins were kept in water which 
was gradually diluted, after some weeks a pair of conical prominences, 
each bearing a single bristle, appeared at the end of the abdomen. 

The experimenter also relates that by breeding salina in still 
more diluted water he attained a form resembling Schaffer's 
genus Branchipus. But the principal difference between the 
genera is that in Artemia the last segment is about twice as 

1 Bateson, Materials, etc., p. 96. 



284 CAUSES OF VARIATION 

long as each of the others, while in Branchipus it is divided. It 
is extremely significant that this division should be produced in 
Artemia by culture in comparatively fresh water, but the fact is 
no warrant for the assertion that one genus can be converted 
into another by altering the environment. It rather casts doubt 
upon the wisdom of a classification which establishes generic dis- 
tinctions upon differences so slight and so easily brought about. 

The same experimenter studied species of the genus Daphnia, 
and found " in their case also considerable structural and physi- 
ological changes, the fresh- and salt-water forms differing, in his 
opinion, by characters usually held to be specific." ^ 

Bateson studied the common cockle, a mollusk, everywhere 
present in the Aral Sea and its outlying waters of different 
degrees of salinity. One of the lakes (Shumish Kul) on its 
western shore exhibited no less than seven distinct terraces, 
held to represent successive stages of the water levels during 
its long period of drying up, with corresponding increase in 
salinity. The most noticeable differences in the shells taken 
from these successive terraces, and presumably due to increas- 
ing salinity, are outlined as follows : ^ 

1. A diminution in the tJiickness of the shells, first apparent 
in the third terrace. In the seventh terrace this change was so 
marked that the shells were almost horny, and their weight was 
not a third of that of the shells from the first two terraces. 

2. Diminution of the size of the beak [with the lowering of 
the level]. 

3. High coloration. [The author does not state which way 
the changes ran, whether up or down the terraces, but he re- 
marks that all the shells of a given terrace were " very nearly 
alike in texture, thickness, and degree of coloration." ] 

4. Grooves between the ribs appearing on the inside of the 
shell as ridges with rectangular faces. 

5. A great diminution in absolute size of the shells on the 
lowest terrace. 

6. Alteration in proportion of length to breadth, ranging 
from I to 0.80 in the shells of the first terrace to i to 0.725 in 
those of the seventh and i to 0.66 on the shores of neighboring 

1 Vernon, Variation in Animals and Plants, p. 275. - Ibid. pp. 275, 276. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 285 

lakes. In view of these facts Bateson remarks, as quoted by 
Vernon/ " It seems almost certain that these conditions are in 
some way the cause of the variations." 

Biological literature is full of similar examples of the char- 
acteristic effects of varying degrees of salinity. The limits of 
space forbid the further pursuit of a subject which might be 
extended almost indefinitely. It may be sufficient to say that 
the specific influence of salinity upon certain characters is, 
beyond a doubt, well established. 

SECTION X — INFLUENCE OF USE AND DISUSE UPON 
DEVELOPMENT 

No fact is better or more generally known than that use stim- 
ulates and disuse dwarfs the development of many organs. To 
say that development is in proportion to use would doubtless 
be true, roughly speaking, of certain parts, as the muscular 
system, secreting glands, etc. It certainly would not be true 
of many others, as hair, feathers, bony skeleton, etc., which 
develop independently of use, and some of which, as hair and 
feathers, involve no activity in the sense in which the term is 
here understood. 

This discussion should be limited to the distinctively active 
parts, and the influence of exercise or the lack of exercise upon 
their development. Of these parts it may fairly be said that 
perfect development is dependent upon, if not proportional to, 
the degree of their use, especially during the earlier stages of 
development. 

The classic illustration from Darwin, showing the leg bones 
of the tame duck and the wing bones of the wild duck to be 
relatively heavier ; the arm of the artisan and the body of the 
athlete ; the training of the track horse ; the marvelous coordi- 
nation of complicated nervous impulse and muscular response 
in the violinist and the pianist, — all these and a multitude of 
similar facts teach clearly that individual development of 
usable parts depends very much upon their early and continuous 
exercise. 

^ Vernon, Variation in Animals and Plants, p. 277. 



286 CAUSES OF VARIATION 

Upper limits of development. In what sense is development 
conditioned upon use ? Docs use simply enable the part to 
attain its normal z.Vi^ proper development, to which it is entitled 
under the laws of heredity, or does it stimulate development 
beyond the normal f 

Some biologists at once assume the latter to be impossible 
and that any unusual appearance is a case of atavism. It is true 
that in times long past there may have existed ducks that walked 
and others that flew more and better than those which Darwin 
examined ; but when did nature produce a running or a trotting 
horse as good as the one of to-day ? To what remote ancestor 
do our violinists and our pianists owe their skill, and what was 
the instrument on which they acquired it ? 

The accompanying cut is a facsimile of a properly attested let- 
ter written with \\\q feet by a young woman twenty-three years 
old who lost both arms at the age of ten. Among her other ac- 
plishments she numbers cutting, sewing (threading her own 
needle), drawing, sweeping, and a great variety of housework. ^ 

Here is a case of putting parts to an entirely new ?ise, 
demanding a nicety of adjustment that was never acquired even 
in one out of a million of the ancestors. Could there be better 
evidence of the fact that few individuals ever use, and there- 
fore few ever develop, more than a fraction of the capacities born 
in them ; that the possibilities of life are seldom realized, and 
that never are all faculties developed to their utmost in any 
single individual ? 

All this is clear but it is not so easy to determine where to 
draw a line and say, " All development below this is due to 
inheritance and all above to use." The truth would seem to be 
that development depends upon both inherent tendencies and 
external conditions affording opportunities for their exercise, 
and that the maximum of development is reached only ivJien 
both are at their optimum. There is much force in the word 
"optimum." Too much exercise, too much food, too much 
temperature, or too much of any of the conditions of life is 
as unfortunate as too little. 

^ The author saw one man who wrote with his feet, but they were attached 
directly to the body, with no legs whatever. 



EXTERNAL liNFLUENCES AS CAUSES OF VARIATION 287 












/i/>~ \^''/u 1^:^-!^ Mo-Y ^/fe/ i\./' .,v^.' -f-f ,i>.-i,-sro ;5t<,<v^^ .'"^^ Wi^ /^"'^ 

^ '^ r ... / ^ • ^ / 

VvT/v- %ii!l«' a^ii!^ ^.^ac- f.^ ^am-»^-^ ,-v~ <;^iiV-;^'CdU!'-i»— ^^^J-ziP -'Ae. 

f /. r 7 " / 

~.t<it© oi India- H, ->ii-t-,', s;. 



•;f/i5/ <«r ) t;^! n "^^feaj-n on her i, 



■\ "Jotarv =i. K ; - ^^- 



^fe-^S^-^Sf";,"':^"^ * \ - •. fr^....^. '<t ^^^^< 






t 



Fig. 30 illustrates the ability of a highly developed part to perform an extremely 
unusual service. The above letter was written with the feet instead of with 
the hands 

It is as futile to attempt to decide whether internal or exter- 
nal circumstances are more helpful in development as it is to 
attempt to say whether food or heat is more essential to life. 
Both are absolutely necessary, and it suffices present purposes 
if the student understands that external conditions, even to the 
matter of exercise, are fundamentally essential to full develop- 
ment, and that the "limiting element" may be found external 
to the organism as well as internal. We shall not be able to 
assert how much is due to each separately, nor can we determine 
the coefficient to be assigned to use and to disuse, but we are 
safe in resting assured that for many parts development is fairly 
proportional to exercise, at least within the limits of inheritance. 



288 CAUSES OF VARIATION 

Disappearing organs. The disappearance of legs from snakes 
and from whales, the lessening of the fore arms of the kangaroo, 
and of the wing of certain birds, the loss of toes from many 
mammals, and rudimentary conditions generally, argue for the 
gradual disappearance of a part that is no longer useful and no 
longer used. 

The first stages of this disappearance can be understood as 
arising through the cessation of selection and the resulting pan- 
mixia,^ by which inheritance is from the general average of the 
whole race, instead of from a selected lot, as heretofore, result- 
ing necessarily in degeneration as compared with a standard 
sustained by rigid selection. Later stages may be explained by 
" reversal of selection," when the hitherto useful organ has not 
only become useless but in some way detrimental. This would 
account for still further degeneracy, and is as far as the princi- 
ple of use and disuse applies.^ 

Space cannot be taken here for the enumeration of instances 
showing the effects of use and disuse. They may be found on 
every hand, and they abound in books on general evolution.^ 

Hypertrophy. Unusual enlargement of a part is technically 
known as hypertrophy. Two kinds are recognized, — functional 
hypertrophy, when a part is enlarged through use ; and com- 
pensating hypertrophy, which takes place when, one organ 
being removed or becoming functionless, another enlarges.^ 

The voluntary muscles of the hand and arm grow large 
through heavy use, but the muscles of the fingers of a musician 
do not undergo hypertrophy, though the total amount of work 
may be very large. It is only when muscular work is done against 
great resistance that enlargement of the muscles takes place. ^ 

1 A term coined by Weismann and denoting " universal crossing," literally 
" all mixed." See Weismann, Essay on Heredity, I, 91, 141 ; also Romanes, Dar- 
win and After Darwin, Part II, pp. 291-306. 

2 For fuller discussion of disappearing organs, see next chapter. 

'^ Darwin, Origin of Species (sixth edition), pp. 1 08-1 12 [D. Appleton & 
Company] ; also Animals and Plants under Domestication (second edition) 
[D. Appleton & Company] : in general, II, 285-293, 345, 346; in rabbits, I, 129- 
134; in ducks, I, 299-301. 

* Morgan, Regeneration, pp. 115-118. 

^ Of course the effects of use are not limited to increase of size ; they are fully 
as noticeable in nicety of adjustment. 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 289 

When one kidney is removed from either man, rabbit, or 
dog, the other becomes enlarged and the total amount of urea 
excreted is unchanged, and this is true even if the removal is 
made at maturity, after the parts have reached their probable 
full development. 

This is allied to the fact that the full amount of urea is 
excreted at once upon the removal of one kidney, proving that 
its fellow is able to increase its labor even before hypertrophy, 
and showing that under normal conditions the kidney is not fully 
worked. There is first an increased flow of blood, then increased 
excretion, then increased size. The same is true of the salivary 
glands, the mammae of the female, the testes of the male, and 
quite likely of paired organs generally. 

When the spleen is removed the " lymphatic glands of other 
parts of the body become enlarged." ^ Another kind of compen- 
sating development is the well-known increase of one faculty 
when another is extinct, as the hearing and the touch of the 
blind. In this instance, as in learning to write with the feet, 
the part is not only developed and trained to its utmost, but 
the undivided attention is fixed upon the matter in hand. 

The student who bestows careful study upon the relation of 
the individual to his environment will arrive at three definite 
conclusions : 

1. The impulse to development and its chief directive forces 
are within. 

2. But the possibilities of that development, in kind as well 
as in degree, lie very largely in surrounding conditions and 
entirely external to the organism. 

3. These surrounding conditions, therefore, while not logically 
causes of variation, since they cannot bring about a development 
whose tendency does not already exist, are yet the limiting ele- 
ments to all development, and many of these conditions are 
chemical and physical forces able to exert strongly directive 
influences upon growth capable of differentiation in more than 
one direction. On this point see also the chapter on " Relative 
Stability and Instability of Living Matter." 

1 Morgan, Regeneration, p. 118. 



290 



CAUSES OF VARIATION 



SlCCnoN XI — I'LXTKRNAL INFLUlONCIvS AS CAUSP:S OF 
VARIATION IN TVIM': 

The studenL must distinguish clearly between the influence 
of external conditions upon an occasional individual and their 
effect upon the type of the race. There are three possible ways 
in which the environment may result in a modification of type : 
(i) by affecting all individuals in the same way; (2) by selec- 
tion ; (3) by the inheritance of the modifications due to condi- 
tions of life. It remains to examine each somewhat carefully. 

All individuals affected in the same manner, thus influencing 
the type directly. The modifying effects of the conditions of life 
have been c|uile fully noted. If but few individuals are affected, 
it is manifest that the type will not be .seriously changed ; but 
if, on the other hand, every individual is affected, and in the 
same way, then the type is to that extent due to the conditions 
of life. 

For example, size is directly influenced by the food supply, 
and increase of size in a race, contemporaneous with a better 
food supply, may fairly be attributed to the favorable influence 
of full feed acting upon all individuals alike. 

Size is also inherited, so that the limits of development are 
due to two influences acting together, — inheritance and food 
supply. It is often exceedingly difficult to determine how much 
to attribute to the one influence and how much to the other. 

What is true of size in this respect is true of every other char- 
acter that is in the slightest degree dependent upon environment 
for its development. Accordingly much uncertainty prevails as 
to the comparative influence of inheritance and environment. 
The racial type can be determined only by the study of the indi- 
viduals constituting the mature population ; but their develop- 
ment is the result of two sets of causes, — the one of heredity, 
the other of environment, — both contributing to the same effect 
and both continuous through life. 

Under the old view every individual was regarded as the re- 
sult not only of what was born into it but also of the direct 
influence of its environment. Individuals constitute the type, 
and so it is that when the conditions of life affect all individuals 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 291 

alike they necessarily influence the type of the race, but to 
what extent cannot be told without some method of subtracting 
the normal results of simple inheritance. No method of doing 
this has ever been discovered, and much uncertainty has always 
prevailed as to what proportion of existing types should be 
credited to the conditions of life. 

The puzzling problem is greatly simplified if we enlarge the 
meaning of the word " inheritance " to cover not only the lines 
of possible development but the full capacity as well. In this 
view of the case the individual and the race are understood 
as possessing hereditary capacities for development far beyond 
that for which opj^ortunities arc likely ever to be afforded by 
environment. This largely removes the conditions of life from 
among \\\ii fundamental causes of variability and relegates them 
to the realm of passive and permissive, though necessary, requi- 
sites for the full display of hereditary power. It tends strongly, 
too, to regard most individuals as something less than would 
be indicated by their hereditary possibilities, and to consider 
environment in general as the limiting, not the stimulating, 
element in development. With this view the writer is inclined 
to agree, though it necessarily reduces the extent of dirrct 
influence of the environment. The student is never to forget 
that, whatever may be the influence of surrounding conditions 
upon one form of life, the same influences affect other species 
differently, thus showing that their characteristic effect is con- 
ditioned upon the power of the organism to react, — a condition 
that is eminently internal and inheritable. 

Selection as a cause of variation in type. Many individuals 
are unable to meet the conditions of life with which they find 
themselves surrounded, and in the attempt become extinct. 
This is selection, and it is manifest that the prevailing type of 
the race as it exists at any moment, being made up of selected 
individuals, is something diffcreiit from that which was born 
into the race. It is also manifest that only a limited portion of 
adults will reproduce, so that selection through the external con- 
ditions of life exerts a strong influence upon type. 

Selection is therefore one of the most powerful — if not the 
most powerful — influences known in the modification of species, 



292 CAUSES OF VARIATION 

and it may be fairly spoken of as a primary cause of variation in 
type. This does not make it, however, Hke temperature or food 
supply, a fundamental cause of variation in living matter. There 
is no basis for selection until differences have appeared from 
other causes. When the selection is made, based on these differ- 
ences, it is certain to affect the type, and it is therefore a cause 
of type variation ; but it was no cause of the original differences 
on which its action was predicated, and it is in no sense an 
original cause of variability. The confusion of mind which causes 
selection to be regarded as a cause of variation has arisen from 
a failure to distinguish clearly between the individual and the 
type, — between the material on which we can work through 
selection on the one hand, and the finished product on the other. 

Variation in type through the inheritance of modifications due 
to environment. Whether individual modifications due to environ- 
ment (acquired characters) are inherited will be discussed in a 
following chapter. It is the purpose here only to show the nature 
of the effect of such inheritance in case it does occur. 

If the modifications due to external influences should per- 
chance be inherited, even in the slightest degree, then the effects 
of modification would, like those of selection, become cumulative, 
and the type would the more rapidly conform to the environment 
and the more rapidly establish a " fit " with the conditions of life. 

It is evident that this is a difficult field. Merely through the 
exigencies of maintenance those characters will develop best that 
are most favored by the conditions of life, thus bringing about 
a kind of mass response to the exactions of the environment. 
Again, by the principle of selection, only those in fair accord with 
the environment will live, and this brings about a still closer fit. 
If, now, modifications due to environment were fully and com- 
pletely inherited, the adjustment to constant conditions would 
speedily become so exact and complete as to leave no room for 
selection. 

Few biologists are bold enough to claim this extreme degree 
of inheritance of modifications due to environment. Many deny 
it in toto. That neither extreme is right is comparatively easy 
of as good proof as we are generally able to bring in affairs bio- 
logical, but where between lies the truth it is most difficult to 



EXTERNAL INFLUENCES AS CAUSES OF VARIATION 293 

determine. The first two causes mentioned, both of which are cer- 
tainly at work, sufficiently explain most phenomena, but whether 
there is an additional fraction due to inheritance, it is most im- 
portant for us to know. 

It can be but a fraction at best, and being in exact line with 
selection and with the direct action of the conditions of life, it is 
exceedingly difficult of identification and of separation from the 
larger causes. If inheritance is to be included, however minute 
the fraction in a single generation, its effect is cumulative, and in 
time it would become the most powerful and irresistible of all 
causes influencing type. Its further consideration must be deferred 
to a later chapter, but the result of its activity, if it has any, is 
in its influence upon type. 

Summary. Though the impulse to development lies within, 
the opportunities for that development and the forces controlling- 
subsequent activities are to be found in the conditions of life 
surrounding the organism. 

These are generally insufficient to afford full development of 
all the possibilities with which the organism is endowed by hered- 
ity. Accordingly the individual does not express in its own per- 
sonality the full extent of its heritage, and individuals generally 
are to be regarded as having realized something less, rather than 
something more, than their birthright. 

Living matter, like non-living matter, sustains definite relations 
to external materials and forces, and the chemical elements of 
which it is composed are not freed from their ordinary reactions 
to other elements or to chemical or physical energies. And so it 
is that living matter is subject to both constructive and destructive 
combinations, and to definite reactions toward gravity, light, tem- 
perature, electricity, and to chemical and physical forces generally. 

Herein lies the modifying effect of surrounding conditions upon 
the development and activities of living matter. Endowed from 
within with definite properties and capacities, their realization 
depends very much upon outside materials and forces which pro- 
vide the conditions under which the definitely organized matter 
is compelled to discharge its activities, and we do well to become 
somewhat familiar with the nature and extent of the limitations 
thus imposed. 



294 CAUSES OF VARIATION 



ADDITIONAL REFERENCES 

Certain Habits of Animals traced to the Arrangement of 
THEIR Hair. By Walter Kidd. Proceedings of the Zoological Society 
of London, II, 145-158. 

Effect of Climate on Sugar Content of Beets. Experiment Station 
Record, XIII, 736. 

Effect of Darkness upon Vegetation. Experiment Station Record, 

XIII, 651. 

Effect of Electricity upon Growth of Plants. Experiment 

Station Record, XIV, 346, 352, 548 ; (Acetylene Gas Light), XIV, 

421, 437; XVI, 137. 
Effect of Humidity on Growth. Experiment Station Record, XII, 

1014. 
Effect of Presence or Absence of Certain Salts upon the 

Composition of the Crop. Experiment Station Record, XIV, 

561-563. 
Effect of Starvation on Plant Growth (first, .shortage of nitrogen ; 

second, shortage of potassium). Experiment Station Record, XIV, 

119. 347- 
Effect of Water Content upon Development of Wheat, Oats, 

Clover, etc. Experiment Station Record, XIII, 125-126, 441-631. 
Experimental Zoology. By J. H. Morgan. Chapters II and III, 

pp. 12-41. 1 
Injurious Effect of Freezing on Development of the Embryo 

IN the Egg of the Hen. Experiment Station Record, XI, 577. 
Variation of Anthrax Bacillus when bred under Different 

Conditions. Experiment Station Record, XIV, 293, 916. 
Variation in Nitrogen Content of Wheat. Experiment Station 

Record, XIII, 451. 
Variation in Tubercle Bacilli when found in Different Envi- 
ronment. Experiment Station Record, XIV, 1121 ; XV, 188. 
Variations caused by Fertilization. Experiment Station Record, 

XIV, 347. 

1 This excellent volume was not yet off the press when this copy was prepared. 
It is especially recommended. 



CHAPTER X 

RELATIVE STABILITY AND INSTABILITY OF LIVING MATTER 

In order to guide the student of breeding in forming his con- 
ceptions as to what may and what may not be accompHshed in 
the way of modifying the form or function of domesticated ani- 
mals and plants, everything is valuable which throws light upon 
the degree of fixedness in living matter ; that is to say, in the 
relations that happen to have become established between the 
essential characters of existing species. 

When the student for a time bestows careful study upon varia- 
tion and comes to realize how radical are some of the departures 
from type and how sweeping are some of the deviations from the 
normal, he is led to feel instinctively that living matter exists in 
a state of extreme instability as regards both form and function, 
and that almost anything is likely to happen. 

When, however, he considers that, through it all, distinct types 
are preserved ; and when he notes the singular persistence of cer- 
tain characters through all the vicissitudes of time and evolution, 
reappearing generation after generation when they were supposed 
to have been long lost, and in many cases lingering after their 
usefulness is past and associated characters have been blotted 
out, — when he considers all this, the careful student will realize 
that stability and instability are relative terms, and he will begin 
seriously to inquire into the degree of stability of the various plans 
upon which matter has been organized and vitalized. It is there- 
fore profitable to inquire somewhat fully into the relative stabil- 
ity or instability of those compounds that are endowed with life, 
and into their relative ability to maintain their integrity and dis- 
charge their functions under conditions both normal and abnormal. 
The utility of this inquiry rests in the light it may throw upon the 
extent to which characters that have become typical are fixed and 
unchangeable, and the extent to which they may be modified. 

295 



296 CAUSES OF VARIATION 

SECTION I — EVIDENCE FROM STABILITY OF TYPE 

Although no two individuals are alike, and although a given 
character differs greatly in different members of the race, yet 
there is a specific type that is always and everywhere present ; 
though the elements are exceedingly variable, yet the resultant 
composite is remarkably constant as compared with other types. 

In other words, when we compare horses with horses we are 
impressed with the fact of variability, but when we compare 
horses with cattle, or even with asses, then we are led to marvel 
at the fixity and persistence of type. In all its variations, the 
horse is still clearly a horse. Wide and profound as is variability, 
it is yet well within limits, and certain types continue with 
singular persistence. 

The Hubbard squash and the Morgan horse are good exam- 
ples of persistence of type. With all the variability of the Cu- 
curbitaceae, the Hubbard squash persists, distinct in type and 
quality. It mixes freely with other types, but its characters are 
evident even then, and it possesses a singular ability to free itself 
from such admixtures and return again to the original. 

The Morgan horse is a breed established by a single animal, 
and yet, a hundred years after the death of Justin Morgan, when 
the per cent of his blood is of necessity slight, the Morgan 
characters still stand out clearly, constituting a type almost as 
distinct as that of any existing breed. This is the solitary known 
instance of the founding of a breed by a single ancestor. It 
illustrates in a peculiar way the occasional extreme persistence 
of a type once formed, and is in marked contrast to the readiness 
with which other types break up and disappear. 

The old-time persistence of the sloping rump in the Berkshire, 
of the narrow chest in the Poland-China, of lack of depth behind 
in the pony-built Hereford, of deficient crops in the Shorthorn, 
— these and similar defects that might be mentioned illustrate 
the strength with which certain characters continue, even in the 
face of the most powerful opposition, and argue strongly for 
stability of type. 

It is also a general fact that species hold their types with 
essential success under a great variety of conditions, both 



RELATIVE STABILITY OF LIVING MATTER 297 

favorable and adverse, yielding but slowly, and sometimes not 
at all, to modifying influences, and often suffering extinction 
when a slight modification would have resulted in preservation. 
Thus the oaks and the tulip tree have come down to us from 
remote ages practically unchanged, and the elephant is with us 
yet, substantially the same as he has been for probably thou- 
sands of years. 

And yet there is constant variation, in these as in more flexi- 
ble species. They have not freed themselves from variability, 
even though the species as a whole has come to be remarkably 
constant. Indeed, the more the question is studied, the more 
evident it becomes that a great deal that passes for variability 
is merely individual fluctuation around a practically stationary 
point, not necessarily involving actual change in type. That 
is to say, few individuals exactly reproduce the type of the 
species, however fixed it may have become ; most of them 
depart slightly this way or that, making a great show of varia- 
tion, so that we seem to be in the midst of bewildering differ- 
ences, even though the type is practically unchanged. In cases 
of this sort deviations represent not so much departiwes from 
type as individual approximations to a general average. 

Here is ground very deceptive to the breeder. Generally 
speaking, variation denotes flexibility of organization, and there- 
fore possibility of improvement, but the breeder must not assume 
that great variation denotes large possibility for improvement. 
Fundamentally it denotes quite as much an inherent failure to 
assume a distinct type; and often a lesser deviation, repre- 
senting a true departure from type, affords a far more favorable 
basis for improvement than do those deviations that after all 
are merely fluctuations about a center that has a strong tend- 
ency to remain fixed. ^ 

1 Pearson believes that the extent of variabihty cannot be reduced more than 
about 1 1 per cent, however rigid the selection. He does not claim that the type 
cannot be shifted more than that amount, but that, however much it may be 
shifted, there is still variability about the new center, and that this variability is 
at least 89 per cent of the original variability of the race. See Pearson, Grammar 
of Science, pp. 481-485; also chapter on "Selection." This subject will be fully 
studied in a succeeding chapter entitled " Type and Variability." 



298 



CAUSES OF VARIATION 



SECTION II — EVIDENCE FROM MUTABILITY 
OF SPECIES 

Species do not, however, always remain unchanged. On the 
contrary, they frequently exhibit a progressive development 
truly marvelous. Horses, for example, are traceable backward 
by easy stages and well-defined connecting links to a time far 
beyond the appearance of man upon the earth, the line ending 



Head 



Fore Foot 



HindFoot 



Teeth 




OneToe 

Splints of 

2nd and 4th 

digits 



OneToe 

Splints of 

2nd and 4th 

digits 



Protohippus 



Mesohippus 



Protorohippus 



Hyracotherium 
(Eohippus) 



ThreeToes 

Side toes 
not touching 
the ground 



ThreeToes 

Side toes 

not touching 

the ground 




Long- 
Crowned, 
Cement- 
covered 



J Three Toes 
Side toes 
touching the 
ground; 
Splint of 5th digit 



Three Toes 

Side toes 

touching the 

ground 



Four Toes 



Short- 
Crowned, 
without 
Cement 



Four Toes 
Splint of 
Jst digit 



Three Toes 
Splint of 
5th digit 



Fig. 31. Comparative drawings of skulls, feet, and teeth of prehistoric horses, 
showing evolutionary development. Reproduced by permission from 
Origin and History of the Horse by H. F. Osborn 

in one of the earliest mammals, a little five-toed creature not 
much larger than the domestic cat. 

No less than twelve stages in this evolution are well known, 
and represented by specimens more or less complete : ^ 

1 William D. Matthew, of the American Museum of Natural History, article 
" Horse, the Evolution of," in Encyclopjedia Americana. This is one of the best 
and one of the newest accounts of the development of the horse, and is chosen be- 
cause of its accessibility and reliability. The outline given, while not marked by 
quotations, is practically an abstract of the reference. 



RELATIVE STABILITY OF LIVINCi MATTER 299 

I. Hyracotherinin. Skull only. Found in London clay of 
the Lower Eocene (earliest mammals). Specimen in British 
Museum. 

2.' EoJiippiis. Much better known, coming from the Lower 
Eocene of Wyoming and New Mexico. Teeth like the former ; 
four toes on the front foot, with a splint of the fifth ; three toes 
behind, with a splint of another, showing that considerable 
departure had already taken place from its evident five-toed 
ancestry. Height of animal 12 to 16 inches. 

3. P^'otoroJiippJis (Wyoming, 1880). Four complete toes in 
front and three behind ; no splints ; skeleton of the size of a 
small dog. Described by Cope as "the four-toed horse." 

4. OroJiippiis. Only parts of jaws and teeth, but these show 
some advance. Specimen at Yale University. 

5. EpiJiippHs (Upper Eocene, New World). Only incomplete 
specimens found, but much time has elapsed and considerable 
development is noted, especially in the teeth. The toes are 
still four and three, but the central toe is " becoming much larger 
than the side toes." 

Collateral branches of the same period in the Old World 
(Paleotherium and Paloplotherium) had three toes of nearly 
equal size on each foot. They were very abundant at this time 
but seem to have become extinct, — a fate that overtook most 
of the branches of this fertile and progressive stem. 

6. MesoJiippiis (White River Formation). Three toes on each 
foot, the middle much the largest, the side toes bearing little 
weight. By this time the animal ranges in size from the coyote 
to the sheep, and the molar teeth are well developed. All parts 
of the skeleton known. Fifth toe represented by a splint. 

7. AncJiitJicrium (Lower Miocene). Found both in Europe 
and in America. Much like its predecessor, but larger, with 
better-developed teeth. May be one of the "side branches" 
rather than in the direct line of the modern horse. 

8. Hypohippiis and Parahippiis. A complete skeleton of Hypo- 
hippus was found, 1901, by the Whitney Expedition near 
Pawnee Butte, Colorado. In the forefoot small rudiments still 
represent the first and fifth toes, but the splints are gone ; 
the second and fourth digits still touch the ground, though 




Fig. 33. Progressive evolution in the horse : the lower figure is a full-sized model 
of the Eohippus in comparison with the skull of the modern horse, showing 
that the skull of the latter horse is larger than the entire body of its ancestor. 
— From specimen in American Museum of Natural History, New York. 
Courtesy of Director H. F. Osborn 



300 



RELATIVE STABILITY OF LIVING MATTER 301 



lightly. The animal was of the size of a Shetland pony, but is 

regarded as being "off the direct 

line of descent." See Fig. 33. 

The companion form, Parahip- 

pus, is regarded as nearer the 

line, having better teeth and 

smaller side toes. 

9 and 10. ProtoJiippus and 
Pliohippus (Middle and Upper 
Miocene). Teeth much im- 
proved as grinders, — the val- 
leys being filled with cement, 
— all showing the appearance 
of harder vegetation. The side 
toes (II and i v) are still complete, 
but do not touch the ground. 
In some species of Pliohippus 
they have almost disappeared. 

11. Hippari n (VWocewe). 
Much like Protohippus, but 
larger, with more complicated 
teeth. Found both in Europe 
and in America, but is probably 
one of the "side branches." 

12. Eqnus (Pleistocene and 
Recent). The modern horse, in 
which digits i and v have en- 
tirely disappeared and 11 and iv 
are represented by splints. 
This single remaining branch of 
the horse family (including the 
asses) has developed one of the 
most specialized of animals. It 
has left behind many unsuc- 
cessful relatives, representing 
departures that proved either 
unprofitable or unfortunate and 
coming thus to a more or less 




Fig. 33. Three-toed ancestor of the 
horse, — the Hypohippus : a complete 
skeleton found in the Middle Mio- 
cene, Colorado, showing the second 
and fourth toes touching the ground 
lightly. — From specimens in the 
American Museum of Natural His- 
tory, New York. Courtesy of Direc- 
tor H. F. Osborn 



302 



CAUSES OF VARIATION 



abrupt end. The modern horse, however, after his long and 
tortuous evolution, seems destined for a prolonged and notable 
existence. During the progressive changes in the feet the 
leg has been greatly lengthened, the joints modified from the 
loose ball and socket to the firmer hinge joint, and the teeth 
have become exceedingly serviceable. It is a noticeable fact 
that the power of a species to withstand the vicissitudes of ex- 
treme lapses of time depends very largely upon the ability of 
its feet, its legs, and its teeth to undergo modification. It has 
been said that the elephant has succeeded in maintaining him- 
self to the present in spite of his feet, and by virtue of his excel- 
lent teeth and his remarkable proboscis. 

It is noticeable that the larger part of this evolutionary his- 
tory of the horse has been worked out from specimens found in 
western America,^ but no one believes that the modern horse 
is an American animal. This evolution seems to have proceeded 
upon substantially parallel lines in the eastern and the western 
continents, which were, during its progress, united by a broad 
strip of land in the region of Alaska; but something seems to 
have happened to the American branch, and it is believed that 
we are indebted to the European and Asiatic branch for the horse 
of the present. 

Indeed, South America is represented by a fossil form {Hip- 
pidium) whose feet resembled Equus, except that they were 
short and stout. Its teeth resembled those of Pliohippus (Museo 
Nacional, Buenos Ay res). This form had evidently advanced 
nearly to that of the present, but perished in the general disaster, 
whatever it was, that overtook the American horse, for it left 
no descendants that persisted until historic times. 

Causes of the evolution of the horse. As is remarked by 
Matthew, " the evolution of the horse, adapting it to live on the 
dry plains, probably went hand in hand with the evolution of 
the plains themselves." At the commencement of mammalian 

1 Our knowledge of the evolution of the horse is largely due to the indefat- 
igable labors of Professor Henry F. Osborn, Director of the American Museum 
of Natural History, and to the magnificent generosity of the late William C. 
Whitney, through which extensive explorations and significant discoveries were 
made in Wyoming and other regions of western America. The student of this 
subject will eagerly await Professor Osborn's forthcoming full report. 



304 



CAUSES OF VARIATION 



life the Mississippi valley was just emerging from the Gulf of 
Mexico, and the plains of western Europe and Asia were low 
and wet. The climate was moist and tropical, stimulating dense 
and luxuriant growth of giant vegetation even as far north as 
Greenland. With the Tertiary came a general elevation, usher- 
ing in a comparatively cold, dry climate, favorable to grasses 
and the harder vegetation generally. With this came grassy 
plains and the evolution of races with good teeth and excellent 
feet and legs, fitting them to a life in the open. 

With these profound changes in nature other forms under- 
went a development similar to that of the ancestors and other 
relatives of the horse. Many of these, as our cattle, sheep, swine, 
etc., developed a two-toed foot, and some, as the rhinoceros, 
stopped at the three-toed stage, but none of them became so 
highly speciahzed as the horse. 

Here was a great line of descent, continuing almost for ages, 
and terminating in many highly specialized species that are still 
flexible. But it gave rise on the way down (or up) to many known, 
and doubtless to many unknown, branches that became extinct 
through some general disaster, or, more likely, because of their 
inherent inability to develop all the characteristics necessary to 
meet changing conditions. For example, as the teeth developed 
into molars fitted for grinding the ever-hardening forage, some 
species secreted cement in the valleys thus supporting the hard 
and grinding ridges; others did not, and it is significant that in 
the latter case no species endured.^ The elephant alone, of his 
kind, has persisted to the present, and if this is because of his 
teeth, and in spite of body and feet, which are ill adapted to 
modern conditions, it serves to show on how slender a thread 
the life of a species often hangs. 

Present existing land species are to be regarded as representing 
lines of descent naturally endowed with an unusually high degree 
of flexibility ; all the more stable and less adaptable forms having 
perished off the earth in the long struggle to keep up with the 

1 It is worthy of remark that the central plains of South America seem to 
have developed a horse-like animal {Litopterna), losing its lateral toes and develop- 
ing the hinge joint and lengthened limb; but it never developed cement in its 
grinders, which remained inferior, and we are not surprised that its line became 
extinct. 



RELATIVE STABILITY OF LIVING MATTER 



305 



evolution of the world as a whole. Existing species therefore 
represent the choicest material of the organic world. Having 
arrived at a high state of differentiation, they have doubtless 
lost something of the flexibility that marked their early and more 
generalized forms, yet they are to be regarded as " highly selected 
material," ready to the breeder's hand for still greater adapta- 
tion, not only to their own needs but to those of man. 

Even when dealing with specially flexible forms, the breeder 
is never to forget that they are constantly giving rise to branches 
that are incapable of adaptation. Unhappy is the breeder who 
devotes his life to a branch of this kind, whether it be among 
horses, cattle, or any of the more slowly multiplying forms, animal 
or plant ; for no amount of apparent variability will make up for 
inherent defects, nor will it, seemingly, avert the evdl day of 
extinction. 

SECTION III — EVIDENCE FROM REVERSION AND 
ATAVISM 1 

The sudden reappearance of a long-lost character serves to 
remind us that combinations once effected tend strongly to 
return. The English breeds of cattle are supposed to have 
descended from the ancient wild white cattle that roamed freely 
over the island until the year 1 200 or later, when private owner- 
ship interfered. With the inclosing of the larger estates as hunt- 
ing parks, herds of these cattle were included with other game 
animals, and for over six hundred years they have lingered in this 
semi-wild condition at Chillingham, Chartley, and other parks. 

1 It is important that the student observe the modem distinction between 
" reversion " and " atavism." They both refer to the reappearance of characters 
once typical but now extinct. " Reversion " is the term to use when the character 
belonged to a near-by ancestor clearly of the same species but several generations 
removed, while " atavism " is used to denote the appearance of characters belonging 
to exceedingly remote ancestors, perhaps even of different species. An example 
of reversion is the occasional appearance of the white color in the red breeds of 
English cattle, and a good example of atavism is the occasional persistence of 
gill slits in mammals, which generally disappear during embryological development 
but occasionally remain as permanent openings. Canine teeth in man, normally 
present, are regarded as a heritage from some primitive ancestor. They may some 
day become atavistic. The term " reversion " covers most of the breeder's needs. 
It is the biologist who deals with remote species. 



306 CAUSES OF VARlATlOiV 

During this time there has been (supposedly) no admixture 
with domesticated herds, and yet there appears occasionally, 
even in a Devon herd, a white calf whose ears, lower legs, and 
brush of tail are marked with the tawny red or brown of the 
wild ancestor, and whose matted, curly hair, upstanding horns, 
and peculiar facial expression bespeak his reversion to the 
early type. 

This singular persistence of characters once typical argues 
strongly for stability if considered from the standpoint of the 
ancient character, but it speaks not less plainly for instability if 
considered from the standpoint of the new (present) type. 

The vermiform appendix, the persistence of the tail in most 
mammals, — these and scores of similar instances attest the 
stubborn resistance of a structural part to the extinction that is 
inevitable ; and the case of the " beard " of the turkey cock 
illustrates the fact that a combination of whatever order, once 
started, tends strongly to continue, even though useless and 
unmeaning. 



SECTION IV — EVIDENCE FROM DISAPPEARANCE 
OF PARTS 

The organic world is full of instances of structural parts 
lingering long after their usefulness has largely or quite disap- 
peared, and after entirely new relations have been established 
among associated characters.^ 

The hind legs of the python and the whale, already rudimen- 
tary and represented only by bones internal to the surface, and 
those of the sea lion and the seal, evidently disappearing in the 
same manner ; the wing of the apteryx, reduced to the merest 
trace hidden in the plumage, and that of the ostrich, plainly fol- 
lowing along to the same fate ; the fetal hair of the whale, and 

1 This is entirely independent of the question of the influence of utility in the 
origin and development of a new character. It has been the fashion to assume 
that none but useful characters will originate. The writer, on the contrary, inclines 
to the belief that any character will arise whose elements are present in the organ- 
ism, quite irrespective of its usefulness, and that it will continue unless prevented 
by selection, although manifestly it will never attain maximum prominence except 
through the cumulative effect of the .selective process. 



RELATIVE STABlLirV OE LIVING MATTER 



323 



but from sheer inability to support life. Manifestly all regener- 
ation is a struggle, and a prerequisite to its accomplishment is 
an assured base of supplies and uninjured vital organs. 

Regeneration by transformation.^ Regeneration in some of 
the lower animals is accomplished through rearrangement of old 
substance as well as through the addition of new material. 






Fig. 39. Regeneration of Stentor cut into three pieces, as at J 

B: this row shows regeneration of anterior piece. C: this row shows regeneration of middle 
piece. D: this row shows regeneration of posterior piece. This regeneration is effected 
first of all by rearrangement of material, — each piece having been supplied with a por- 
tion of the nucleus. — After Morgan, from Gruber 

If a short piece be cut from the stem of a hydra the first step 
in the formation of a new individual from the piece is the closing 
of the ends and a shrinking of diameter, thus making a closed cylin- 
der, but much smaller than the stem from which it was cut. In 
a day or two four tentacles appear at one end, and shortly the 
piece has assumed the characteristic form and propot'tions of a 
complete hydra, after which it may increase in size. The same 
is true of a piece of a planarian or of a Stentor (see Fig. 39). 

1 Morgan, Regeneration, pp. 13-15. 



324 CAUSES OF VARIATION 

The first process seems to be to assume the characteristic 
form, afterward to increase in size ; not only that, but regenera- 
tion is possible in the entire absence of food, as will be seen 
later, — all of which indicates a more or less extensive trafisfor- 
viation of material. 

Regeneration in embryos and eggs.^ There is much reason to 
believe that regeneration, especially by rearrangement, is more 
pronounced in the embryonic than in the adult state. The frog 
does not regenerate the leg, but the tadpole does. If the blastula 
of the sea urchin be cut into two pieces, each will develop into a 
perfect, but abnormally small, embryo. If the parts be separated 
at the two- or the four-celled stage, each is capable of developing 
into a perfect embryo, but at the eight-celled stage they are not 
capable of such development. 

If each cell of the two-celled stage is capable of developing 
into a complete individual, then the material at this stage must 
be indifferent, that is undifferentiated. In other words, if the 
first cleavage be considered as dividing into right and left halves, 
and each half is capable of developing into a whole, the case is 
exactly like that of regeneration in the split planarian ; if, how- 
ever, the first segmentation be considered as dividing into ante- 
rior and posterior regions, and if each may develop an individual, 
it is exactly similar to the case of the regeneration of a worm 
that has been cut in two crosswise into anterior and posterior 
halves. In all cases some readjustment of material is involved. 

This separation is easily effected in the sea urchin by shaking, 
in which case each part, below the eight-celled stage, develops an 
individual. If in the frog the parts, even at the two-celled stage, 
be separated, each collapses ; if instead one half be killed by a 
needle, the uninjured part develops at first a Jialf embryo, after- 
wards making more or less successful " post generation " of a 
whole embryo.^ It is therefore a perfectly well-established fact 
that, in certain species at least, a part of an Qgg or embryo is 
capable of developing into a perfect individual. 

To what extent this separation of segmenting eggs at the 
two-celled stage may take place in nature is of course unknown, 

1 Morgan, Regeneration, p. i8; also chap. .\i, pp. 216-241. 
■^ Ibid. pp. 216-221. 



RELATIVE STABILITY OF LIVING MATTER 325 

but it has been assumed to be the cause of the production of 
such twins as are exceedingly similar. Hypothetical cases of this 
sort are known as "identical twins," supposedly arising from a 
single ovum instead of from two. 

Experiments upon a variety of species show different powers 
of development from part embryos. Wilson found, and Morgan 
verified the fact, that in Amphioxus each of the first two or four 
cells could develop an entire embryo, and that the one to eight 
blastomeres would develop to the blastula stage but no farther. 
Zoja showed that the isolated blastomeres in a number of jelly- 
fish developed each a whole embryo but of small size.^ Driesch 
studied the matter in ascidians and found the cleavage of iso- 
lated blastomeres to be neither like that of the whole embryo 
nor like the development they would each have undergone had 
they remained in place. They produce symmetrical gastrulae 
and larvae of small size, but lacking in certain parts? 

No one can avoid the conclusion that the phenomena of re- 
generation generally show an extreme stability of living mat- 
ter; but they also betray, especially in lower organisms and in the 
developing embryo, an unexpected elasticity. To assign absolute 
stability or extreme instability to living matter would be to state 
but half the truth. A fair interpretation of the facts of regen- 
eration leads to the conviction that living matter has the power 
of extreme readjustment in its effort to discharge its normal func- 
tions, and that it will discharge those functions as nearly as may 
be, even under dire distress, and even though important details 
of structure are by force omitted.. 

Regeneration in plants. This is different from regeneration 
in animals in that " the piece does not complete itself at the cut 
end, nor does it change its form into that of a new plant, but 
the leaf buds that are present on the piece begin to develop, 
especially those near the distal end of the piece." ^ The processes 
are similar in the two cases in that a piece may give rise to a 
vv^hole individual, as when the begonia leaf throws out first roots 
and then stems, which develop into perfect plants. 

Regeneration in higher animals. It is a somewhat singular fact 
that the lower animals possess larger powers of regeneration of lost 

1 Morgan, Regeneration, p. 237. 2 Ibid. p. 236. ^ ibid. p. 15. 



326 CAUSES OF VARLVnON 

parts than do those which are more highly differentiated. Still 
the latter are not destitute of this faculty of replacement. The 
teeth of many vertebrates are shed once and replaced ; rarely a 
second replacement occurs. If the ox loses the horn, the loss is 
permanent ; but the stag sheds his annually, each successive pair 
arising from the same scar or bud, but each provided with an 
additional prong. By what inherent quality of this particular 
spot are we to explain this annual change in the character of 
the part restored } 

Birds shed their plumage, and many animals their hair, annu- 
ally, as trees shed their leaves, and often the new growth dif- 
fers materially from the old. The " milk teeth " are simpler than 
the permanent set ; the color of the foal and the fawn changes 
with maturity ; and the shape of the cotyledon gives little indi- 
cation of what the real leaf will be. Nobody seeing the umbrella- 
like first leaf of the basswood would suspect what the later 
leaves will be, nor would one suspect the clover until the "third 
leaf " appears. 

Repair of injury among higher animals seems to be exceed- 
ingly limited. However, wounded muscles can " fill up " to some 
extent ; cut nerves mend slowly ; severed blood vessels repair 
themselves and restore circulation to the part ; liver, kidney, 
glands, and tissues generally have sufficient power of regenera- 
tion to close wounds and to replace lost portions more or less 
perfectly, but nearly always with a scar ; broken bones will knit 
or a small piece removed will be restored, but an entire bone cut 
off will not be replaced. Of all parts the skin possesses the highest 
power of restoration, probably because it is normally in active 
growth from beneath to replace the parts worn off from above. 

The character of the regenerated part. The regenerated part 
may compare with the original in any one of four different ways : 

1. It may be exactly like the original, as in the leg of a sala- 
mander (holomorphosis). 

2. It may be like the original except smaller in size (mero- 
morphosis). 

3. It may be different from the original but like some other 
part of the body, as when an antenna replaces an eye (hetero- 
morphosis). 



RELATIVE STABILITY OF LIVING MATTER 327 

4. It may be unlike any normal structure of the body, as when 
a new leg is " unlike any other leg on the body " ^ (neomorphosis). 

With respect to the tissues from which- regenerated parts arise 
two distinct cases are to be noted : 

1. Where the part regenerated springs from tissue of the 
same kind, requiring only an extension of growth, as when an 
injured muscle is repaired. 

2. Where the regenerated part springs from tissue of a totally 
different order, as where a severed leg is restored from the cut 
outward, or where the lens of an eye arises from the iris, re- 
quiring differentiation as well as growth.^ This subject will be 
pursued further under the section on " Origin of New Cells and 
Tissues." 

Effect of temperature upon regeneration.'^ Planarians were cut 
in two transversely at the pharyn.x. No regeneration took place 
below 3° C. Of six specimens kept at this temperature only 
one regenerated, and that incompletely, the eyes and brain 
being incomplete after six months. The temperature at which 
regeneration took place most rapidly was 29.7°, at which a new 
head formed in four and six-tenths days. At 31.5° it required 
eight and a half days to complete the head ; at 32° regeneration 
commenced, but death occurred in about six days; at 33° re- 
generation was slight, and at 34° none took place, death occur- 
ring within three days. Other species showed a similar range 
for optimum, minimum, and maximum.* 

Influence of food upon regeneration.-^ While regeneration takes 
place more rapidly with a full food supply, it nevertheless pro- 
ceeds without it. In this case the new growth appears to be de- 
rived not from surplus food material but from the protoplasm 
itself, resulting in reduction in size. 

If a planarian be kept for several months without food, in 
this starved condition it gradually shrinks in size, even to one 
thirteenth of the normal (see Fig. 40). 

If a starved worm be cut in two pieces, each will regenerate, 
though more slowly than if fed, the new part increasing in size 
at the expense of the old. 

1 Morgan, Regeneration, p. 24. ^ ibid. pp. 26-27. ^ Ibid. pp. 27-29. 

- Ibid. p. 205. * Ibid. pp. 26-27. 



328 



CAUSES OF VARIATION 



As Morgan remarks, ^ " The growth of the new part at the 
expense of the old tissues is a phenomenon of the greatest im- 
portance, an explanation of which will involve, I think, the most 
fundamental questions pertaining to growth." To this remark it 
may be added that the phenomenon is also of the greatest impor- 
tance in its bearing upon the relative stability of living matter. 
In so far as protoplasm is zvorked over to serve new purposes, it 
shows wonderful elasticity ; but the fact that 
the organism preserves or completes its plan 
at almost any expense, even to itself, betrays 
a wonderful persistence on the part of the 
original plan. 

It is known that the starving cat or dog 
will replace a large share of the dry matter 
of the body with water, and sacrifice all other 
activities to the vital processes. Plants grow- 
ing with no nitrogen supply save what is 
contained in the seeds will soon reach the 
maximum of possible development, but will 
continue to produce new leaves at the ex- 
pense of the old ones,"^ as the rapidly grow- 
ing stalk of the century plant feeds on its 
thickened leaves, or the beet and carrot feed 
on their thickened roots. 

Effects of light upon regeneration.'^ In the 
case of plants only * does light seem to affect 
regeneration, and in them the influence 
appears to be confined to the blue rays. 
" Herbst observed that when the eye of cer- 
tain Crustacea is cut off, sometimes an eye and sometimes an 
antenna is regenerated." Experiments were conducted to see 
whether lio-ht might be the factor which determined whether the 




Fig. 40. Effect of star- 
vation upon the pla- 
narian 

A, well-fed worm ; B, the 
same individual after 
being kept without food 
for four months and 
thirteen days. — After 
Morgan 



1 Morgan, Regeneration, pp. 27-29. 

2 The writer saw the original clover plants in the first Rothamsted series for test- 
ing the nitrogen-gathering powers of root tubercles. One of these plants had no 
source of nitrogen but the seed. It was two years old, still producing new leaves 
as the old ones died down, but it had never blossomed, nor was it able to pro- 
duce more than four leaves at any time. 

3 Morgan, Regeneration, pp. 29-30. ^ Ibid. p. 78. 



RELATIVE STABILITY OF LIVING MATTER 329 

eye or the antenna should appear, but as many eyes were regener- 
ated in the dark as in the light. It was found, however, by both 
Herbst and Morgan independently, that "when the end only of 
the eyestalk is cut off an eye regenerates, but when the eyestalk 
is cut off at the base an antenna regenerates." ^ 

Effect of gravity upon regeneration. The effect of gravity upon 
regeneration in plants is pronounced,^ but only one case is known 
of its influence upon regeneration in animals. This is the case of 
the hydroid Aiitcnnnlaria antoiniiia^ 

This animal, however, has many of the characteristics of the 
plant, for it lives attached by a kind of root to the bottom of 
the sea, and its general form is that of a branching stem, like a 
typical plant. All experiments show that regeneration in this 
form is always with reference to gravity, much as in the case of 
plants. Whatever the position of the piece, the new growth is 
upward from the most elevated part, ivJiciher basal or apical, and 
downward from the lower extremity and from the base of the 
new growth (see Fig. 41). 

The effect of gravity upon regeneration in plants may be 
briefly summarized as follows : * 

1. If a piece of stem of the willow be suspended with its 
apex upward, in three or four days roots will spring from small 
swellings at the basal ^ end, and three or four buds will arise at 
the apical ^end, the one at the extreme tip coming first and grow- 
ing fastest, others in regular decreasing order (see Fig. 26, A). 

2. If the piece is long the lower buds will not start, but if it 
should be cut in two pieces, or if a ring of bark should be cut from 
the middle, each would behave as already described, showing 
that any point on the stem may throw out either shoots or roots, 
according to its position with reference to the cut and to gravity. 

3. These new growths generally arise from preexisting buds 
if the piece is young, but they may arise from regions entirely 
destitute of preexisting buds. The writer knew a red maple tree 

^ Morgan, Regeneration, p. 30. - Ibid. pp. 71-80. ^ Ibid. pp. 30-32. 

* The pieces e.xperimented upon were suspended in moist atmosphere. 

5 In all these explanations "basal" means the end that was down when the 
plant was in its normal position, whatever its position during the experiment. 
" Apical" refers to the end farthest from the base in nature. 



130 



CAUSES OF VARIATION 



in Urbana, Illinois, eighteen inches or more in diameter. It 
forked about six feet from the ground. A heavy storm split 
one of the limbs away, when it was found that a dense net- 
work of roots had formed in the moist soil that had collected 
in the fork. 




Fig. 41. Regeneration in response to gravity in animal organisms : this creature 
{^Anteiuiitlnria anteitnind) resembles plants in its habit of growth, being 
attached ; it also resembles them in its response to gravity in regeneration. 
— After Morgan, from Loeb 

4. If the piece be suspended apex down, the shoots will still 
start from the apical end, bending upward, and roots will start 
not only from the basal end, now uppermost, but they will start 
from the whole length of the stem and bend downward, showing 
that the force determining whether shoot or root shall be put out 



RELATIVE STABILITY OF LIVING MATTER 331 

is largely internal, but that the influence determining the direc- 
tion of the growth is external, — gravity (see Fig. 26, B). 

5. This "polar difference " is most energetic in j^t^//;/^ stems, 
gradually lessening in older growth, though the tendency remains 
in quite old pieces. 

6. If internodes only are used, some plants will regenerate 
and others will not ; but if they do regenerate, the tendency is 
for roots to appear from the basal end and leaves from the apical, 
whatever the position.^ 

7. If a piece of the root of a poplar be suspended vertically in 
a moist chamber, apex downward, leaves and shoots will appear 
from the basal^ now the upper, end ; if suspended basal end 
downward, the shoots will still arise from this (basal) end.^ 

8. Certain plants, as the begonia, are able to produce new 
plants from even a single leaf'ii set in moist sand. In all cases, 
so far as known, roots first arise at the base of the leaf stem, or 
midrib section, and later shoots arise on the apical side of the 
roots, whatever the position. 

9. Curiously, if the leaf be taken from a begonia just ready 
to flower, the new plant will flower very quickly after becoming 
estabhshed, but with few leaves and little growth ; but if it be 
taken from a plant just out of flower, the growth will be greater 
and the period longer before flowering follows. 

10. When pieces of stem are suspended vertically, apex up- 
ward, polarity and gravity act together ; when suspended apex 
downward they act oppositely. The two forces may, to some 
extent, be separated by employing different positions. For ex- 
ample, if the piece be held obliquely, apical end the higher, the 
buds along the upper side will develop more than those on the 
lower side ; and if it be placed horizontally, all the buds on what 
is now the upper side of the stem will start, but those at the 
apical end will grow more rapidly. 

If held in an oblique position with basal end higher, differ- 
ent results follow ; but in general it is shown that where polarity 

1 Morgan, Regeneration, p. 74. 

2 It should Ije remembered that the basal end of the root is the end nearest 
the stem. 

3 Morgan, Regeneration, p. 75. 



332 



CAUSES OF VARIATION 



and gravity are opposed to each other the former is by far the 
stronger force. ^ 

II. If a long piece of stem be suspended by both ends, roots 
will start freely along the curved loxvcr surface of the bent stem. 
If now the bent stem be reversed, roots will not only form less 
freely, but they will mostly be along the loiver or under side of 
the arch, the concave instead of the convex side of the curve, 
and clustered closer to the basal end.^ 

SECTION vni — INTERNAL FACTORS IN REGENERATION 

Even among plants it is noticeable that internal influences 
are strongly involved in the regenerative processes. Indeed, 
one point of difference between plants and animals is that the 
latter regenerate directly from the cut surface, while the former 
regenerate by means of buds thrown out at the side and just 
behind the point of severance. 

Again, it is to be observed that those organisms whose 
regeneration is influenced by gravity are the attached species, 
that maintain habitual and constant relations to gravity, but that 
those species which, like most animals, move about freely, 
regenerate according to internal influences, except in so far 
as vital processes are involved through food, temperature, or 
chemical conditions. In other words, the study of regeneration 
is essentially a study of internal forces, and even among plants 
subject to the influence of gravity the internal factors are yet 
the dominant ones. They are well worth study, therefore, as 
bearing upon the subject of this chapter and upon the inherent 
forces of organized and living matter. 

Polarity and heteromorphosis. If a short piece be cut from 
the anterior end of an earthworm the main piece regenerates 
promptly, the small piece with difficulty or not at all ; and the 
same is true as to the posterior end. Again, if the short piece 
regenerate at all, it does not complete itself by growing a new 
worm, but by growing a reversed head (or tail) like itself, so 
that we may have an individual with two heads and no tail, or 
vice versa. In other words, the polarity is reversed ; for if the 

1 Morgan, Regeneration, p. 78. ^ i^jid. pp. 7(5-80. 



RELATIVE STABILITY OF LIVING MATTER 



worm had been cut in the middle, both halves would have pro- 
duced an entire worm, minus, perhaps, certain parts like the 
reproductive organs, which do not seem to be reproduced. How- 
ever, the posterior half of a planarian will regenerate, producing 
an entire worm with typical eyes. 

What it is that determines the character 
of the restored part is a mystery. A worm 
is cut at a certain point. The tissue of 
one piece will regenerate head with all its 
parts, and the tissue of the other, at the 
same point, will regenerate posterior parts, 
— unless the cut be well forward, when 
both pieces will regenerate aiiterior parts, 
or well back, when botJi will regenerate pos- 
terior parts. 

These facts cannot be explained on the 
theory of "formative stuffs," because head 
tissue may arise from posterior positions 
and tail tissue from anterior. For exam- 
ple, if an oblique cut be made into the 
side of a planarian, head tissue will arise if 
the cut be directed backward, even though 
made well to the rear, while tail tissue will 
arise from a cut directed forward, even 
though made at a point so far ahead that 
if carried entirely across the body it would 
sever a piece so small that it would give 
rise to Jiead tissue only (see Fig. 42). 

The determining cause of these oppo- 
site differentiations is yet a mystery. 

Lateral regeneration. " Since the most 
familiar cases of regeneration are those that 
take place at the anterior and posterior 
ends, we not unnaturally come to think of polarity as a phenom- 
enon connected only with the long axis of the animal, but 
there are also many cases of lateral regeneration in which a 
similar relation can be shown." ^ 

1 Morgan, Regeneration, p. 43. 




Fig. 42. rdarity in re- 
generation : regenera- 
tion from the two 
oblique cuts opening 
forward will produce 
" head stuff," though 
one cut is far posterior; 
on the other hand, an 
anterior cleft opening 
backward produces 
tail matter. — After 
Morgan 



334 



CAUSES OF VARIATION 




If an incision be made in the side of an actinian, tentacles 
will arise at that point, and they will seize pieces of meat and 
press them against the stem, whether a mouth was formed or 
not ^ (see Fig. 43). 

If a planarian be split lengthwise into right and left halves, 
regeneration takes place whether the halves be equal or unequal. 
The completed worm will be at first both nanvivcr and shorter 

than the normal, but with time and 
feed it will equal or even exceed 
the original. How the nerve cords 
and genital ducts are formed anew, 
especially from the piece so far to 
one side as to include none of their 
substance, is a mystery closely akin 
to that of original differentiation 
from the fertilized ovum. If the 
slice be taken well to one side, no 
head matter is included. In such 
a case the head appears first at 
the side of the piece, but later it 
assumes its proper position. 

Regeneration from an oblique 
surface. If the tail of a tadpole 
be removed by an oblique cut, 
the regenerated tail will at first 
stand at rigJit angles to the cut and obliquely to the axis of the 
tail. As growth proceeds, however, the tail gradually swings 
into line with the axis of the body. 

If the head of a planarian be removed by an oblique cut, it will 
begin to regenerate at the forward part, making the head at first 
stand at rigJit angles to the cut, and not in line with the body. 

If a piece be taken from the middle of a planarian by two 
parallel but oblique cuts (for example, running backward from 
left to right), the head will begin to regenerate from the anterior 
end at its forward (left) side, while the tail will begin at the 
posterior extremity but on the opposite side, the final result being 
complete restoration of the normal shape. 

^ Loeb, Physiology of the Brain, p. 52. 



Fig. 43. Lateral regeneration : a cut 
in the side of an actinian produced 
a clump of tentacles which would 
seize a piece of meat and press it 
against the side of the body, even 
though no mouth were present. — 
After Loeb 



RELATIVE STABlLirV OF LIVING MAITER 335 

That the new material produced in regeneration is at first 
totipotent — that is, capable of more than one differentiation — 
is easily shown. If a short piece be cut from the middle of a 
planarian, and if, after the new material has begun to form, the 
whole mass be split lengthwise, both halves will develop heads 
directly ; but if the split is not made " until just before the 
formation of a head, then each half piece produces at first a 
half head, that completes itself later at the cut side." ^ 

Again, if the head be cut from a planarian and the body be 
split for a distance, the split will heal and a single head will 
regenerate ; but if a slice be taken out of the middle line of the 
body, or if otherwise the two pieces be prevented from fusing, 
then tzvo heads will regenerate, one on each piece. ^ These two 
heads may later pull apart with sufficient force to tear the body.^ 

All these phenomena reveal great capability of readjustment 
as to more or less differentiated tissue. The more the matter is 
studied the more we discover that the line between regeneration 
and development is one of degree rather than of kind, and that 
differentiation in both cases, whether normal or abnormal, rests 
upon causes very imperfectly understood but closely akin to 
those of differentiation in general. 

SECTION IX — EVIDENCE FROM GRAFTING 

When tissue of one kind, plant or animal, is removed from 
its connections and set into tissue of the same or of a different 
kind, and a union takes place so that growth ensues, the union is 
called a graft. From our standpoint no little interest attaches to 
the variety of conditions under which grafts may be effected, and 
to the fact that the growth upon the graft is like the part set in 
and not like the tissue that supports it, — the host acts only as 
affording standing room and food supply to the graft. Again, if 
two dissimilar pieces are joined, each preserves its identity. 

Grafting is comparatively easy among plants, though the species 
that may be joined are limited. Among animals it is more dififi- 
cult, but by no means impossible. 

1 Morgan, Regeneration, p. 49. ^ Ibid. p. 50. 

3 Loeb, Physiology of the Brain, p. 82. 



336 CAUSES OF VARIATION 

Born succeeded in uniting" tadpoles of two different species of 
frogs, Rana esculcnta for the anterior part and R. arvalis for the 
posterior. This "made-up" animal lived seventeen days. Harrison 
succeeded in keeping an individual made up of R. vircscens and 
R.paliistris until its transformation from a tadpole into a frog.^ 

In the same way earthworms may be built up of two or more 
individuals of the same or of different species, and the pieces used 
in this building up may even be reversed, so that the middle part 
of the made-up worm may have its posterior part placed anteri- 
orly, or the reverse. Worms may be made with two heads, with 
or without a tail, or with two tails, with or without a head, — 
though the latter, for obvious reasons, can live but a short time.^ 

Ribbert grafted a portion of mammary gland into the ear of 
the guinea pig, where it grew, and when the pig became pregnant 
the grafted tissue secreted 7nilk? 

The whole subject of grafting, even more than that of regen- 
eration, shows the wonderfully persistent nature of differentiated 
tissue, though it shows also the variety of conditions under which 
its activities may be discharged. 

SECTION X — EVIDENCE FROM THE ORIGIN OF NEW 
CELLS AND TISSUES 

New tissue may arise in regeneration in three distinct ways : 

1 . It may arise from tissue of its own kind ; that is, the tissue 
produced in regeneration may arise from the same kind of tissue 
in the organism. 

2. It may arise, not from like tissue, — of which none may be 
present, — but from the same point of origin and in the same 
manner as during embryonic development. 

3. It may arise from a source entirely different from that of 
embryonic development, and in this case may be either normal 
or heteromorphic. 

Examples of the first class are everywhere at hand ; indeed, 
this is the most ordinary form of regeneration, and many have 
erroneously supposed it to be the only form. Ordinarily, muscle 

1 Morgan, Regeneration, pp. 184-185. ^ ibid. pp. 1 71-173. 

•^ Loeb, Physiology of the Brain, p. 206 



RELATIVE STABILITY OF LIVING MATTER 337 

gives rise to muscle, nerve to nerve, bone to bone, and each part 
to its own kind by the simple method of growth extension. 

This, however, is the simplest method of regeneration, and 
more complex methods are necessary in extreme regeneration, 
where the entire supply of certain tissues is cut away, and the 
new growth must arise from different tissue or not at all. 

Examples of the second class are less common, but not rare. 
Where an entire limb is gone regeneration must proceed upon a 
plan different from the one it would follow were only a single 
tissue involved, like a wounded muscle. The first new growth 
that arises must in some way be endowed with the power of pro- 
ducing not one, but many, dijfcrcnt kinds of tissues. Gotte, as 
quoted by Morgan, has studied both "the embryonic development 
and the regeneration of the limb of triton, especially in regard to 
the origin of the new bones. He found that the skeleton develops 
in much the same way in the embryonic limb and in the regener- 
ating limb, and the process in the latter may be said to repeat that 
in the former." If the larva is young, the new growth differs but 
little from the old, but if the bones had become ossified, the 
difference between the two is much more marked.^ Curiously 
enough the salamander regenerates the tail completely, bones 
and all, but the regenerated tail of a lizard contains not a new 
series of bones, but a cartilaginous tube which is attached to the 
broken seventh caudal vertebra.^ 

An example of the third case, in which tissue is regenerated 
from a source dijferent from t/iat of cmbryonie development, is 
shown in the reproduction of the lens of the eye of the salamander 
or of triton. In this case, if the lens be removed a new one is re- 
generated from the upper edge of tJie iris, a part of the body from 
which the lens of the eye never develops normally in the em- 
bryo of this or of any other vertebrate. In the embryo the lens 
develops from the ectoderm at the side of the head, having no 
connection with the iris. 

The regeneration from like tissue is no more difficult of com- 
prehension than is ordinary growth, and that which repeats the 

1 Morgan, Regeneration, pp. 200-20 r. 

2 Ibid. p. 198. The lizard's tail does not break between the two vertebrae, which 
are strongly joined, but in the middle of the vertebra, which is relatively weak. 



338 CAUSES OF VARIATION 

course of embryonic development is involved in the mystery of 
ordinary differentiation from totipotent or indifferent tissue ; but 
regenerated matter which arises from tissue in no ivisc involved 
in embryonic dcvclopnient would seem to be outside of the influ- 
ence of heredity. In the latter case it may result in normal tis- 
sue, as in the lens of the eye, or in heteromorphic growth, as in 
the production of an antenna instead of an eye, or of a foot instead 
of an antenna. 

SECTION XI — EVIDENCE FROM DEVELOPMENT AND 
DIFFERENTIATION ^ 

From the fertilized ovum to the fully differentiated adult in- 
dividual of the highest species is a long step. Nothing is more 
evident than that all this differentiation is the res?ilt of forces 
resident luithiu the single cell of the ovnni. Whatever office is 
discharged by outside agencies, and whatever deviations or modi- 
fications are produced thereby, the impulse to differentiate and 
the direction of differentiation arise from forces internal to the 
organism. Moreover, this differentiation, great as it is in the 
finished product, when traced backward merges by imperceptible 
shades each into the next preceding, until the undifferentiated 
ovum is reached at the end (or beginning) of the series. 

What is the nature of these internal forces, and what are the 
agencies that set them in motion, are the chief mysteries in ani- 
mal and plant development. That a single germ cell, similar in 
its essential nature to any one of the tissue cells of which the 
body is composed, — that such a cell " can carry with it the sum 
total of the heritage of the species, that it can in the course of 
a few days or weeks give rise to a mollusk or a man, is the 
greatest marvel of biological science."^ 

" In attempting to analyze the problems that it involves," con- 
tinues Wilson, " we must from the outset hold fast to the fact 
on which Huxley insisted, that the wonderful formative energy of 
the germ is not impressed upon it from without, but is inherent 
in the Qgg as a heritage from the parental life of which it was 
originally a part. The development of the embryo is nothing new. 

1 Wilson, The Cell, p. 430. 2 ibid. p. 396. 



RELATIVE STABILITY OF LIVING MATTER 339 

It involves no breach of continuity, and is but a continuation of 
the vital processes going on in the parental body. What gives 
development its marvelous character is the rapidity with which 
it proceeds, and the diversity of the results attained in a span 
so brief." 

We can define the chief mystery of development as lying in 
the facts of differentiation and definite tcnniiiation to growth, but 
if we ask lioio the impulses governing such complicated results lie 
latent in a single cell, and Juno they operate in orderly sequence 
beginning and ending at the proper moment, we have asked the 
" final question," and " in approaching it," says Wilson, " we may 
as well make a frank confession of ignorance." 

About all we can hope to do in the present state of knowledge 
is to throw light upon the question of comparative stability of 
organized matter and note the conditions under which one kind 
of cell gives rise to another of a different order. On this point 
certain facts of development have an important bearing. 

Cell division. All differentiation during development is by 
cleavage of the germ cell. The phenomena of division and mito- 
sis are in general the same in the cleavage of the germ cell and 
the development of the embryo as in the division of ordinary 
tissue cells, except that the body cells for the most part give 
rise only to others like tliemselves, while those of the germ and 
the embryo give rise not only to others like themselves but to 
ina7iy different kinds as well. 

This distinction is relative rather than absolute, for we remem- 
ber that in certain species a small part, even a leaf, is able by 
regeneration to give rise to a new individual, involving differen- 
tiation similar if not equal to that of embryonic development. 
However, in many species and with most tissues the power of 
typical differentiation appears to be lost in the first development. 
In this connection it is well to remind ourselves that in many 
species the amount of chromatin matter in the somatic cells is 
different from that in the germ cells. ^ 

Geometrical character of cleavage. The earliest cleavage of 
the germ cell is governed by two definite geometric principles 
announced by Sachs: (i) the cell typically tends to divide into 

^ Wilson, The Cell, p. 426 (concerning Boveri's investigations on Ascaris). 



340 



CAUSES OF VARIATION 



equal parts ; (2) each new plane of division tends to intersect 
the preceding one at a right angle. ^ 

A typical cleavage of a spherical egg v^ould be, first, vertical, 
dividing into right and left halves ; second, also vertical, but at 
right angles to the first, dividing into dorsal and ventral portions; 
third, horizontal, dividing into anterior and posterior parts ; — 
after which all sorts of irregularities might be expected, including 
cleavages parallel with the surface, cutting in two the long cells 
that formerly extended to the center. The Qgg of the holothu- 
rian, like those of Synapta, proceeds regularly until as many as 
512 cells are reached,'^ while others become irregular almost at 
once, some quadrants dividing much more rapidly than others. 

Variation in the rate of division. If division proceeds with 
perfect regularity, the number of cells will of course form an 
increasing geometrical series whose ratio is two, — 2, 4, 8, 16, 
32, 64, 128, 256, 512, 1024, etc. Such a series has been men- 
tioned, extending to 512. 

This uniform series is rarely realized, however, owing to irreg- 
ularities in the rate of division ; for example. Nereis regularly 
gives rise to the series 2, 4, 8, 16, 20, 23, 29, 32, 37, 38, 41, 42, 
" after which the order is more or less variable." ^ 

In some portions of the dividing cell the cleavage proceeds 
therefore with much greater rapidity than in others, nor is the plan 
uniform in all cases, though the results achieved may be sub- 
stantially identical. In general the rate of division is most rapid 
in the upper hemisphere of the ovum, and in some instances it pro- 
ceeds very slowly, with long pauses, in the lower, giving great 
irregularity in the size of cells. 

Temporary effect of outside influences upon cleavage. Driesch 
placed eggs of sea urchins under pressure sufficient to flatten the 
spheres to disks. In this position "the amphiasters all assume 
the position of least resistance, i.e. parallel to the flattened sides, 
and the egg segments as a flat plate of eight, sixteen, or thirty- 
two cells. This is totally different from the normal form of 
cleavage ; yet such eggs zv/ien released from pressure are capable 
of development and give rise to normal ejnbryos." ^ Without 

1 Wilson, The Cell, p. 362. ^ ibid. p. 366. 

- Ibid. p. 364. * Ibid. p. 375. Italics are mine. 



RELATIVE STABILITY OF LIVING MATTER 341 

doubt in nature similar temporary effects are caused by internal 
stress or pressure of the parts of the egg itself. 

After noting other causes of irregularity, Wilson fittingly 
observes : 

All these considerations drive us to the view that the simpler mechanical 
factors, such as pressure, form, and the like, are subordinate to far more 
subtle and complex operations involved in the general development of the 
organism. . . . We cannot comprehend the forms of cleavage without refer- 
eticc to the end results. ^ 

Promorphology of the ovum. Is there something in the origi- 
nal shape or character of the egg that corresponds to the fin- 
ished individual ? Is there a polarity of the ^gg that is in any 
way related to the order of cleavage and the axis of the body ? 

Speaking of the eggs of insects, Wilson says : '^ 

In a large number of cases the egg is elongated and bilaterally sym- 
metrical, and, according to Blochmann and Wheeler, may even show a 
bilateral distribution of the yolk corresponding with the bilaterality of 
the ovum. 

Hallez is here quoted as asserting, after a study of the cock- 
roach, water beetle, and the locust, that " the egg cell possesses 
the same orientation as the maternal organism that produces it ; 
it has a cephalic pole and a caudal pole ; a right side and a left ; 
a dorsal aspect and a ventral ; and these different aspects of the 
&gg coincide with the corresponding aspects of the embryo." 
Wheeler, after studying some thirty different species of insects, 
reached the same result, and concluded that even when the egg 
approaches the spherical form the symmetry still exists, though 
obscured.^ 

In species other than insects the &gg often has a bilateral 
symmetry of its own, " sometimes so clearly marked that the 
exact position of the embryo may be predicted in the unferti- 
lized Qggr'^ 

Polarity of the ovum. It is now well known that in the seg- 
menting eggs of the frog the first two cleavage planes are vertical, 
the first corresponding to the median plane of the body and set- 
ting off right and left halves (which develop into corresponding 

1 Wilson, The Cell, pp. 376-377. ^ Ibid. pp. 383-384. ^ Ibid. p. 3S4. 



342 



CAUSES OF \'ARIATION 



parts of the body), the second setting off dorsal and ventral 
areas ; while the third, which is horizontal, divides into anterior 
and posterior portions. 

The process is the same in many species, and " wherever the 
egg axis can be determined by the accumulation of the deuto- 
plasm in the loivcr hemisphere the egg nucleus sooner or later lies 
eccentrically in the upper hemisphere, and the polar bodies are 
formed at the upper pole ^ 

In such cases of distinct polarity the cleavage planes are prac- 
tically predetermined, and the products of division have each 
their definite role in development. Thus the upper hemisphere 
(so-called animal pole) is the seat of most active division, with 
smaller cells, which develop into cerebral, dorsal, and anterior 
portions of the body ; while the lower hemisphere (vegetable or 
nutritive pole) divides more slowly, its cells are larger, and they 
develop into the alimentary organs and the posterior and ventral 
parts generally.^ 

While this rule is not absolute in all species, it yet indicates a 
broad general principle that lies at the very threshold of devel- 
opment ; namely, that the original i^npulse to direction of growth 
lies in the polarity of the ovum. 

Cause of polarity in the ovum. Gravity would seem to be the 
controlling cause in establishing a kind of polarity in the ovum. 
The nucleus being of low specific gravity, tends to lie eccentrically 
nearer the upper side of the ovum, and the heavier deutoplasm 
settles to the lower side, the parts arranging themselves accord- 
ing to relative weight, like starch granules or other cell contents. 
Moreover, Born has shown that " if frogs' eggs be fastened in 
an abnormal position, — e.g. upside down or on the side, — 
rearrangement of the egg material fakes place " and " a nczv axis 
is established iti the egg.'"^ Schultze discovered that "if the egg 
be turned upside down when in the two-celled stage a whole 
embryo (or half of a double embryo) may arise from each blasto- 
mere, instead of a half embryo as in the normal development, 
and that the axes of these embryos show no constant relation 
to one another." ^ Morgan learned that " either a half embryo 

1 Wilson, The Cell, pp. 37S, 379. 

2 Ibid. p. 422. 



RELx\TlVE STABILITY OF LIVING MATTER 343 

or a whole half-sized dwarf might be formed, according to the 
position of the h/astonicre." ^ 

Causes of differentiation. These facts show : 

1. That a primary cause of differentiation Hes in the polarity 
of the ovum. 

2. That this polarity is due primarily to gravity separating 
its heavier from its lighter parts. 

3. That the Qgg is at first, in many cases at least, indifferent, 
and that its polarity may even be changed after having once 
been well established. 

4. That if the segmenting ovum may be separated into its 
blastomeres, and each may produce a complete individual (Am- 
phioxus, etc.),^ then the egg as a whole is not only totipotent 
but its earlier segments as well are each capable of producing 
all the parts of the body. 

5. The polarity and the development of a part are influenced 
largely by its position with reference to other and especially 
larger parts. 

Roux found that when, in the two-celled stage of the frog's egg, 
one of the blastomeres was killed by a hot needle, the remaining 
one developed a half embryo,'^ whereas in many cases a single 
blastomere is known to be entirely capable of producing a whole 
embryo if freed from its neighbors. 

Again, a section from an earthworm tends to regenerate 
head matter at its anterior end and tail matter at its posterior 
end ; but if a small piece be grafted, even in a reversed position, 
on the anterior end of a larger piece, it will regenerate head 
matter y>v;« its posterior extremity, showing how the polarity of 
the smaller piece is, so to speak, overcome by that of the larger.* 

A consideration of these facts leads Wilson to quote Hertwig 
as follows : The relative position of a blastomere in the whole 
[assemblage] determines in general zvhat develops from it ; if its 
position be changed, it gives rise to something different ; in other 
zvords, its prospective value is a function of its position:" 

1 The different cells of the earlier cleavages (the 2-, 4,8-, i6-celled stages, etc.) 
are known as blastomeres. 

- Wilson, The Cell, p. 423. * Morgan, Regeneration, p. 8. 

3 Ibid. p. 380. s Wilson, The Cell, p. 415. 



344 



CAUSES OF VARIATION 



6. Whether the above statement is absolutely or only rela- 
tively true, the fact is clear that living matter will often go 
through its changes and complete its cycle of development 
under extreme hardship. For example, in some species a blas- 
tomere from the two- or from the four-celled stage may develop 
into a whole (dwarf) embryo or into a half embryo, while in 
others (ctenophore) each one of the first eight may develop into 
a symmetrical and therefore complete individual, but lacking the 
full normal number of stvimming plates} 

7. The conclusion is unavoidable that living matter is endowed 
with wonderful elasticity and persistence of plan, or an approxi- 
mation to it, even under most adverse conditions, providing only 
these conditions do not destroy life. 

And so we return to the original questions : How much of 
what the individual is to be is due to inheritance t How flex- 
ible is the plan 1 To what extent are modifications possible, and 
to what extent are variations inherited } 

Summary. In general the facts of differentiation and of regen- 
eration, together with the persistence of an established type in 
carrying forward inherited qualities even under most adverse 
conditions, indicate extreme stability of living matter. 

On the other hand, the facts of acclimatization argue for the 
alterability of protoplasm, both as to constitution and as to func- 
tion, inclining one strongly to the belief that such alteration may 
become more or less permanent with the organism. 

Altogether the conviction is forced upon us that the activities 
of living matter proceed upon a plan inspired from within and 
arising from the nature of the organization, but that this plan 
has accommodated itself to surrounding conditions in the past 
and is entirely competent to do so again whenever sufficient 
occasion arises, provided only that the new demands be not too 
sweeping or too suddenly imposed. 

These facts need to be constantly in the mind of the farmer, 
who must be prepared for comparatively sweeping changes from 
apparently slight causes. 

We pass now to a discussion of the question as to whether or 
not individual modifications may be transmitted. 

1 Wilson, The Cell, p. 41S. 



RELATIVE STABILITY OF LHING MATTER 345 

ADDITIONAL REFERENCES 

A Natural Hybrid. Experiment Station Record, XV, 677. 

Effect of Stock upon Scion. Experiment Station Record, XV, 363. 

Experimental Zoology. By T. H. Morgan. Chapters XV-XXII, pp. 

239-346. 
Grafting Beets. (Colors that do not blend.) Experiment Station Record, 

XIV, 353- 
Grafting Experiments with Tadpoles. By R. G. Harrison. Science, 

VII, 198-199. 
Influence of Stock upon Scion. By T. J. Burrill, Transactions of the 

Illinois Horticultural Society, 1898, pp. 62-72. Experiment Station 

Record, XI, 51, 152, 250. 
Influence of Stock upon Scion. Experiment Station Record, VII, 

309- 
Modifications in Parasitized Cells. Experiment Station Record, 

XIV, 121. 
Regeneration of Begonia. Experiment Station Record, XIV, 528. 
Resemblance between Cells of Malignant Growths in Man 

AND Normal Reproductive Tissue. Proceedings of the Royal 

Society, LXXII, 499-504. 
Variability of Organisms and of their Elements. Science, X\', 

1-5. 



Part III — Transmission 



Up to this point the study has been confined to the nature 
and kinds of variations that may arise, together with the causes 
that lead to their appearance. We come now to inquire zvJiether, 
and to what extent, these variations are transniissib/e. 

This is the all-important question, because variations that 
are not transmitted are manifestly of no consequence except 
to the individual. Whether desirable or undesirable, they have 
no opportunity to affect the race as a whole either favorably 
or unfavorably. We may therefore disregard, in all questions of 
race improvement, any and all deviations that are not trans- 
missible. 

Those that are transmitted, however, are by that fact destined 
to exert a more or less permanent influence for good or evil. 
Accordingly we cannot know too much about this class of vari- 
ations and the circumstances under which they descend from 
generation to generation and ultimately come to characterize, if 
not to dominate, the type of the race. 

The student, and the breeder as well, is likely to become con- 
fused by the ceaseless panorama of characters and variations 
presented to his view as generations come and go, involving 
sometimes literally multitudes of individuals of all shades of 
difference. He must learn to pass this procession before his 
mental vision with the full realization that a large portion of all 
that he sees will have no permanent influence upon the race. 
He must become acute in detecting the significant factors, which 
are those only that are connected with transmission. 

The study of race improvement is, therefore, essentially a 
study of the laws that govern transmission, — all that has gone 
before being preparatory to that study. Upon two questions 
the breeder must fix his attention, — What is transmitted, and 
how is the transmission accomplished ? 

347 



CHAPTER XI 

TRANSMISSION OF MODIFICATIONS DUE TO EXTERNAL 
INFLUENCES 

SECTION I — INTRODUCTORY 

In the discussion of the causes of variation a clear distinction 
was made between causes internal and causes external to the 
organism. This distinction should still be borne in mind, though 
the principal discussion and all of the controversy arise in con- 
nection with external causes. 

Variations due to causes internal to the germ are transmitted. 
So far as the writer is aware, no one has ever disputed, or even 
questioned, the correctness of this proposition. It is fundamental, 
if not axiomatic, that any change taking place in the structure 
of the germinal matter, which is passed on from generation 
to generation, which is the bearer of all characters and the 
exclusive basis of all transmission, — that any such alteration 
will of necessity make itself manifest at once, and indefinitely 
afterward ; indeed, as long as the change in the constitution of 
the germ continues. This is the purpose of all selective mating, 
— to secure a germ endowed with as many as possible of what 
are considered to be desirable variations, tending to maximum 
development, and as few as possible that are undesirable, and 
these with a minimum development. Such a germ should 
develop an embryo, and finally an adult individual, with the 
highest obtainable degree of excellence. 

To control the germ is the purpose of all selection. It is the 
object of all breeding. We practice line breeding, and even 
in-breeding, to give intensity along certain lines ; we resort to 
mixed breeding, even to cross breeding, to introduce new vari- 
ations and to endow the race with greater flexibility. 

It is in the germ that mutations arise. The causes are 
obscure, but it is here, in the constitution of the germinal 

348 



TRANSMISSION OF MODIFICATIONS 349 

matter, that they are at work, and it is here that races are 
enriched, almost miraculously, with new and valuable endow- 
ments, — not frequently and freely, but occasionally and spar- 
ingly. These are the free gift of nature, arising, so far as we 
can now see, spontaneously, but due, as we firmly believe, to 
definite influences at work within the germ, which is the avenue 
of all transmissible variations. 

Remembering, then, that all influences that affect the germ 
will give rise to variations, we come now to the direct question 
of the chapter, — Are the modifying effects of external influences 
transmitted .'' or does each generation begin anew, unhampered 
and unhelped by the direct effects of previous environment, 
whether favorable or unfavorable } 

The main question. This is an exceedingly important matter ; 
indeed, no other question in all evolution is of such immediate 
and far-reaching consequence in thremmatology. This is because 
the influences of environment are insidious and at the same 
time well-nigh irresistible. If their effects are also transmis- 
sible, they will become, like compound interest or any other 
geometrical progression, strongly and rapidly cumulative, and 
therefore tremendously powerful either for good or for evil. 

This is the old and hotly contested question of " inheritance 
of acquired characters," better stated for our purposes in the 
form. Are the effects of environment transmitted .'' It is but 
fair to warn the student that this is at once the most difficult 
and the most complicated of all the questions of evolution, and 
that not only must its study be critically conducted but the 
student must be constantly mindful of certain fundamental 
considerations, a few of which it will be well to note before 
proceeding to the discussion of the main question. 

What is a deviation ? What we call a variation, a devia- 
tion, or a modification, is not, like a character, an entity that 
can be transmitted. It is rather the degree to which a character 
attains, as measured from the general mean or average of the 
race as a whole. When we speak, therefore, of the trans- 
mission of a variation or a modification, we mean literally the 
transmission of the character as modified, either by internal or 
external causes. 



350 TRANSMISSION- 

Strictly speaking, therefore, it is the cliaracter, and not its 
modification, which is transmitted, and what we desire to know, 
is, whether the modification of a character in a particular indi- 
vidual tends to become permanent ; that is t(^ say, whether a 
character that has undergone modification will be transmitted in 
its modified ox in its unmodified ii^xxw. 

In this connection the student must be I'emintletl that we 
have no way of judging what characters or what modifications 
are boni into an individual except by the development they 
attain in his own personality after reaching the adult stage.' 

For example, when noting an average individual we cannot say 
whether he is one that was exceptionally well born, with fair 
opportunities for development ; whether he was only faii-ly well 
born, but with exceptional opportunities ; or whether he is an 
average both as to birth and opportunity. All three combina- 
tions would produce about an average individual. 

On the contrary, if he be an exceptional individual, we arc 
fairly safe in assuming that he was both well boi-n and well con- 
ditioned ; but if lie be one of the lowest individuals, that he was 
badly born and has lived under hard conditions, — both of which, 
operating together, make even an average development impossible. 

Of a mature individual we may say, first, that all the evident 
characters of which he stands ]:)ossessed were born into him, 
but that the deve/opmeut they have attained is partly a matter 
of birth and partly a matter of the external conditions of life. 
His difference in develojjment as compared with the mean of the 
race taken at the adult stage is his deviation or variation {for 
we use the terms interchangeably), and the question we are now 
asking is. Are these individual deviations transmitted, or are all 
characters transmitted according to a dead level of inheritance, 
leaving all deviations to be accounted for as matters of individual 
attainment through more or less successful development .'' 

Adaptations. The modifying effect of the conditions of life 
is so profound that in nature everywhere both animals and 
plants harmonize with their environment almost perfectly, thus 

1 When tlie individual becomes a breeder his inherited qualities will be fairly 
well indicated by his powers of transmission. In this way an animal truly may 
'' Ijreed better than he is himself." 



TRANSMISSION OK MODIFICATIONS 35 1 

giving the appearance of having been specially created for their 
particular surrouiulings. We know enough of the causes of 
variation, however, to realize thai this " fit " between the animal 
or the plant and its enviroinnent has been brought about by the 
direct action of outside conditions upon organisms somewhat 
plastic and capable of becoming adapted to a wide range ol 
circumstances, — all individuals not possessing this adaptability 
having long since disappeared by natural selection. 

Nothing is more simple and natural than to assume that 
when the individual has acc|uired some modification through 
the influence of the environment it will transmit this modifica- 
tion to its descendants, and that what was at liist impressed 
from without gradually becomes hereditary, exhibiting all the 
cumulative effect (.)f transmissible c|ualities. All appearances 
are in favor of such an assumption, and it is the simplest and 
most direct explanation of the [)henomena of adaptation and of 
the well-known harmony that always exists between a species 
and its environment. 

But there are at least two otJicr methods by which the envi- 
ronment impresses itself strongly upon the species, — both of 
which are always at work, both of which achieve large results 
of an exactly similar character and appearance, and which must 
therefore be either subtracted or fully accounted for before we 
are warranted in assuming results due to direct transmission. 

The first of these is the direct effect of the conditions of life 
acting separately upon all the indixiduals of each generation 
and all in the same direction. This has all the af^pcarance of 
transmission, but it is not cumulative, and can bring about no 
better adaptation in the species, and no greater total change, 
than can be wrought for each individual during its lifetime. 
The other is due to the selective effect of the environment, 
which is cumulative, and, so far as we can see, abundantly able 
to account for all the phenomena of adaptation and for the full 
effects of environment. 

The environment always selective. Some individuals of every 
generation fail utterly to endure the conditions of life and, thus 
failing, they leave no descendants. The next generation, there- 
fore, being descended from the more adaptable individuals, is 



35' 



TRAiNSMlSSION 



more nearly in harmony with the environment, and this cumu- 
lative influence, constantly exerted, generation after genera- 
tion, slowly but surely modifies the race in tJic direetion of the 
enviromneiit, giving again the appearance of inherited modifica- 
tions. Now in nature this selective influence is always at work, 
sometimes by actually destroying the less adaptive individuals, 
more often by affecting not life, but fertility or longevity, or 
both, through little-noticed but insidious agencies. 

This is, moreover, the most powerful of all the means by 
which environment influences species. It entirely outstrips the 
results of direct influences upon individuals, and is fully able 
to account for all ordinary cases of environmental influence.^ 

The source of the difficulty. Here is an ever-present, all- 
powerful influence, bending species into harmony with their en- 
vironment, and its effects must be fully eliminated or accounted 
for before we can determine whether a residue remains to be 
attributed to direct transmission. This is the source of the 
greatest difficulty in attempting to learn whether modifications 
are directly transmitted. 

This selective process of the environment results in the indi- 
rect transmission of such modifications as increase the chances 
of the individual in the struggle for existence; but what farmers 
want to know is whether modifications produced by the con- 
ditions of life are directly transmitted as such, — independently 
of the question whether they increase or decrease the chances 
of life in the individual, and independently of all questions of 
selection. 



1 T/te individiial and the type. The student must be clear as to what consti- 
tutes type. Every individual must be considered with reference to at least two 
generations, the one to which it belongs and the next. The type of a race at any 
particular moment is fixed by the personal qualities of all its adult members, and 
for this purpose all individuals are of equal weight, and one character or differ- 
ence is as good as another. Everything counts in fixing the type of an existing 
generation. 

But when the next generation is considered, it is not so. Only those individuals 
count which succeed in reproducing, and only those differences count that are 
transmissible. The initial or natural type, therefore, as secured by transmission, 
is somewhat different in succeeding generations, nor is it ever fully expressed in 
adult memliers. The existing and visible type of any race is, therefore, at best 
but an incomplete expression of its possibilities. 



TRANSMISSION OF MODIFICATIONS 353 

In nature, where selection is unlimited, it does not greatly 
matter whether modifications thus induced are directly or indi- 
rectly transmitted, — the only difference is a slight one in the 
amount of time required; but among domesticated species, where 
selection is largely controlled, where it is to be employed for as 
few purposes as possible, and where at most, for economic rea- 
sons, its use must be sparing as compared with that of nature, 
— here it is important to know, if possible, whether there exists, 
side by side with our selection, this other influence, in some cases 
assisting, in others opposing, our aims. 

The influence of the environment upon transmission is cer- 
tainly slight at any moment, but if it exists at all it is cumulative, 
and, being independent of selection, it is a friend to the breeder 
for fixing desirable characters, as it is also an insidious enemy, to 
be greatly dreaded, when an undesirable character is involved. 

As the discussion proceeds the student must realize that we 
are looking for that which is at best but an infinitesimal incre- 
ment as compared with the larger results due to selection, the 
presence and influence of which he must grow skillful in detect- 
ing and assessing. 

He must also be upon his guard against evidence that is not 
evidence. For example, a cat learns to open a door, or a mare 
to hold up her foot for her feed. If the young develop the same 
habit as the mother, the hasty observer calls it a case of the 
inheritance of an acquired character ; whereas the truth is that 
in all probability the young creatures simply learned it by obser- 
vation; indeed the readiness of the young to learn by imitation 
is vastly underrated. In the case of the horse it must also be 
remembered that most individuals that hold up the foot when 
begging have defective voices. This defect is extremely likely 
to be transmitted to the young, which, finding themselves voice- 
less, would, if left to themselves, even entirely without example, 
resort to the next most convenient and natural method of beg- 
ging, which is holding up the foot. It must not be forgotten 
that, in the horse, holding up the foot in begging is a kind of 
fundamental instinct, second only to vocal effort, and it may 
be said in general that if a horse cannot call for his feed he 
will hold up his foot. Against such instances as these, urged 



354 TRANSMISSION 

as proof of the inheritance of acquired characters, the student 
must be on his constant guard, and he must be extremely care- 
ful in the generalizations he allows himself to make in this partic- 
ular field of study. 

This subject has been greatly complicated by a mass of tradi- 
tion that has grown up around it. The average man assumes 
that the effects of environment arc transmitted. He does not 
stop to inquire seriously into the subject. He considers all 
doubt on this point as foolishness ; but that which he considers 
as good proof is, in many cases at least, anything but proof. 

As if this were not enough, the naturalist on his part has still 
further muddled the matter by a most unfortunate and con- 
fusing, not to say inaccurate, use of terms. Traditions may be 
ignored for purposes of study, but not so with terminology, 
which should be exact and accurate. The two most unfortunate 
terms that ever crept into evolutionary studies are " congenital " 
and " acquired." 

Characters congenital and acquired. It is a custom with 
evolutionists to assume that every adult individual is in posses- 
sion of two kinds of characters : first, those which were born 
into it (the congenital) ; second, those which were forced upon 
it by the conditions of life or picked up as the result of experi- 
ence (the acquired). They then proceed to the very natural 
assumption that the congenital characters, having been derived 
by inheritance, will in turn be transmitted ; after which they 
raise what would seem to be the final question, Are the 
acquired characters transmitted } Thus is the field of discus- 
sion staked out, and no such battle royal (of words) was ever 
fought out in modern times — except over questions theological 
— as has been waged over the question of the inheritance (or 
transmission) of acquired characters.^ 

1 This is the question that has divided the neo-Lamarckians and the neo- 
Dai-winians, and almost the entire host of evolutionists for the last twenty years 
have ranged themselves on one side or the other of this dispute and have 
allowed themselves to be identified with one or the other of the hostile camps. 

As the special opponent of the theory of the transmission of acquired char- 
acters, the student should read Weismann, particularly his Essays on Heredity, 
his Germ Plasm, and his Germinal Selection. 

The most vigorous and accessible, if not the most able, champion of the 
transmissionists is perhaps Romanes in his E.xamination of Weismannism and 



TRANSMISSION OF MODIFICATIONS 355 

The writer does not propose to enter the disputed territory 
at this point, for the reason that he does not beheve in accept- 
ing for these purposes the fundamental distinction between 
"congenital" and "acquired" characters. The use of the term 
"congenital" as distinct from "acquired" is most unfortunate. 
Any character present at birth is, by definition, congenital. The 
list would include not only the characters typical of the race but 
also malformations and deformities due to conditions in utero or 
to unknown causes. Thus men have been born without feet, yet 
the chances of transmitting the deformity are extremely remote. 
An arm or a leg may be misplaced during embryonic develop- 
ment and malformations result without essentially bearing upon 
the conditions that are supposed to control inheritance. 

Manifestly the most profitable distinction to observe regard- 
ing the inheritance of variations is a strict discrimination be- 
tween those that have arisen through causes affectitig the germ 
plasm directly, on the one hand (blastogenic), and those that 
affect the body during its development, upon the other (somato- 
genic). Now an accident to the embryo in utero is as much 
external to the germ plasm — the inherited substance on which 
development depends — as is an accident after birth, and there- 
fore distinctions between congenital and acquired characters are 
extremely misleading, especially among mammals ; less so, of 
course, among birds, in which no such thing as birth exists. 

his Darwin and After Darwin. Cope, in his Primary Factors of Organic Evolution, 
may be read with profit, as may Eimer in Organic Evolution. 

Both factions claim to be disciples and exponents of Danvin, but the opponents 
of transmission, from their extreme appeal to selection, have come to be known as 
neo-Darwinians, and the advocates of transmission have accepted the name of 
neo-Lamarckians, from their belief in the formative influence of the environment, 
which was the distinguishing feature of Lamarck's view of evolution. 

In general it may be said that, while there are many notable exceptions, the 
zoologists tend to side with the neo-Darwinians against the idea of transmission, 
while the botanists, dealing with fixed and of necessity much more plastic forms, 
tend to go with the neo-Lamarckians. 

In the opinion of the writer, Lloyd Morgan is by far the most satisfactory 
investigator and writer on this vexed question, especially in his Habit and 
Instinct, which should be read by every careful student of this subject. The 
inquiry is conducted to find out the truth, not to prove or to disprove the 
inheritance of acquired characters, and his conclusions as stated on pages 307-322 
of that volume may well engage the attention of the thoughtful reader, whatever 
his personal views on the points in dispute. 



356 TRANSMISSION 

In every case, bird or mammal, plant or animal, the new indi- 
vidual begins with \^& fertilized germ, not at some later period 
called birth ; and for our purposes the distinction should not be 
whether the variation was implanted before or after birth, but 
whether its cause was internal or external to the germ. 

Attention should be fixed upon the germ plasm, the physical 
basis of life and the only known avenue of transmission from 
one generation to the next, and the distinction should be clearly 
made between variations due to changes in its structure from 
internal or other causes, and those changes of the organism 
due to influences exerted directly upon the organism during its 
development. As this discussion proceeds it should be clearly 
borne in mind that no character can be transmitted, no matter 
how strongly present, iinless the ge?'mimil matter is i)i some way 
previously affected. Nothing else passes over from parent to 
offspring, and no other medium of transmission is possible. The 
study is, therefore, clearly defined. Do modifications, as such, 
affect the germ directly, and so become transmitted ; or, if not, 
do the same influences that affect the developing individual 
also affect the germinal matter in the same direction, giving all 
descendants an initial trend or modification similar to the one 
impressed upon the parent ? 

SECTION II — EVIDENCE FROM THE NATURE OF 
VARIATION 

In the opinion of the writer it is fundamentally wrong, both 
logically and biologically, to conceive of the individual as made 
up of two sets of faculties, — one inherited and the other 
acquired. The distinction not only does not rest upon good 
ground, but in its application to the facts of life it leads to most 
unfortunate conceptions and to most erroneous conclusions. It 
is this fundamental misconception of the function of the environ- 
ment that is responsible for most of the foggy thinking which 
marks the contention over the question of inheritance of acquired 
characters, and which nowhere else bears such unfortunate fruit 
as in the field of practical affairs. In general evolution it does 
not matter greatly whether acquired (.?) characters are inherited 



TRANSMISSION OF MODIFICATIONS 



357 



much or little, or not at all ; the discussion is there largely an 
academic question. But in the fields and yards of the farmer it 
is the largest of all questions, and we are led to inquire sharply 
whether these distinctions are real ; whether the differences 
between germinal (blastogenic) and acquired (somatogenic) char- 
acters are differences in kind or in degree ; whether, in short, 
acquired characters, in the common acceptation of the term and 
in any true sense, exist at all. 

The characters of the individual are the characters of the race. 
Careful observation will disclose the fact that every quality 
mJierited or acquired by an adult individual is possessed in some 
degree by every other normal adult individual of the same race. 
All horses can trot some ; all cows give some milk ; all sheep 
bear wool of some color, length, or degree of fineness ; all hens 
have feathers ; all men not idiotic can learn and speak a lan- 
guage; all men have some little (perhaps very little) musical 
ability, and all can learn to play the piano or the violin. The 
point here is not whether it is skillfully done, but whether it 
can be done at all. 

It is a habit of speech to designate a low degree of quality by 
negative terms, and we say of the horse that trots but slowly or 
awkwardly that he " cannot trot." We mean by that that he 
cannot trot well enough to make him valuable for this purpose. 
In the same way the man who " cannot sing " is the one whose 
singing we do not care to hear; the man who "cannot speak" 
is the one on whom we would not depend for the presentation 
of a difificult case. We do not mean of him that, like the oyster, 
he cannot convey information and is dumb because of the utter 
absence of the organs and powers of speech. 

So these are relative terms, like "heat" and "cold," but our 
use of them in the absolute sense has built up in the popular 
mind an assumption that they stand for realities, not relative 
values of the same thing ; just as the unlearned man supposes 
cold to be as real as heat, and black (which is the absence of all 
color) to be as real as white (which is the presence of all). Thus 
have we by our verbiage elevated relative values to absolute 
distinctions in kind, creating misconceptions which we must first 
undo if we are to proceed safely in this study. All individuals 



358 



TRANSMISSION 



of the same raee possess the same cJiaractcrs ; herein do racial 
values exist and hereby are racial distinctions established. 

Variation practically confined to racial characters. In all the 
examples of variation that have been cited, — and they have 
purposely been many, — and in all the cases that occur in our 
fields and yards, variation is confined to racial characters. This 
is the experience of breeders everywhere. When dealing with 
cattle breeding all variation is of cattle characters. We do not 
expect and we do not find among cattle the appearance of char- 
acters belonging to horses, sheep, pigs, dogs, or chickens, — 
except as they are possessed in common. The same is true of 
other species, and when characters are possessed in common 
the variation in each case is well within the range of the species 
in question. 

That is to say, variations in cattle all appear among well- 
known and long-established characters that distinctly belong to 
cattle, such as the head, horns, legs, color, udder, quantity or 
quality of milk, etc. Among chickens the variations are among 
chicken characters, such as the shape and color of feathers ; size, 
color, and quality of the Qgg ; quality of meat, etc. 

We find neither chicken characters appearing among cattle 
nor cattle characters appearing among chickens. The hen can- 
not give milk, nor can the cow bear feathers. There is no inter- 
change of characters between species, either by birth or by 
acquisition afterward. Not only that, but even when the same 
character is possessed by two distinct species its variations in 
each are well ivithin the 7'ange of the particular species. For 
example, the legs of cattle and chickens are built upon the same 
general plan, but they have drifted far apart, and do not overlap 
even in their variations. The leg of a horse and the leg of a cow 
are on nearly the same plan, and yet no one would mistake the 
one for the other, no matter what the range of variation. Even 
color deviations are always within certain definite limits. 

No such thing as an acquired character. Variation is, there- 
fore, a condition, not a thing. It is the state of a racial character, 
not the result of the introduction of a new one ; indeed, variation 
by the introduction of a positively new character is, if not 
unknown among us, a matter that belongs to general evolution 



TRANSMISSION OF MODIFICATIONS 359 

and to the origin of races. It is not a matter that practically 
concerns the thremmatologist, who is working with established 
races and characters whose variations are fairly well circum- 
scribed. The appearance of a positively new character among 
any of these races would be cause for profound astonishment. 
Under the present state of knowledge, and for our purposes, 
we may say that there are no such things as acquired charac- 
.ters, in any proper sense of the term. It is a figure of speech 
at best, and a most unfortunate one, at that. 

By " acquired character," as the term is commonly employed, 
is always meant one of two things, — (i) differences in the 
degree of development of ordinary racial characters, or (2) the 
peculiar use to which the individual has put his natural endow- 
ments under his special conditions of life. 

These are differences in degree, not in kitid. To speak of 
them as characters is to dignify them with a term whose mean- 
ing is eminently qualitative, not quantitative, and this it is that 
has built up the false conception that individuals of the same 
breed or race differ from each other in something that is real ; 
that individual differences are all qualitative, — whereas, within 
the race, they are quantitative merely. 

To speak of these differences, which are only differences in 
degree of development of ordinary racial characters, or at most 
only differences in behavior of organs and parts known to be 
able to respond to various stimuli and to function somewhat 
differently under different conditions, — to speak of differences 
such as these personal acquisitions as acquired characters, is 
to use the term "character" in an unfortunate and singularly 
misleading sense. 

Now a difference which is nothing more than a degree of 
development of a well-known character is not in itself a neiv 
character. It is not in that sense an acquisition. It is more 
in the nature of a realization of what was before a potential 
possibility. 

Neither is a Jiabit entitled to the term " new," or " acquired," 
character. Habit refers only to the customary use of natural 
faculties. Some characters, like those associated with the pro- 
duction of the gastric juice, for example, have but a narrow 



36o TRANSMISSION" 

functional range and are quite out of control of the individual ; 
others, like the brain and the hand, are capable of functioning 
in many directions, — so many that no lifetime is long enough, 
or its needs and experiences varied enough, to exhaust their 
possibilities. 

If the student hopes to follow the mazes of racial characters as 
they traverse the generations, like threads through the patterns 
of a fabric, he must not confuse either his terminology or hi.^ 
ideas by attaching so important a conception as "character" 
to what is nothing more than an individual manifestation of 
character development, or the particular personal use to w^hich 
many racial characters may be put. 

The faculties of the individual are limited in kind to the 
faculties of the race, and in degree to the intensity of their 
inheritance and the conditions of life. There is no case in 
which an individual of one race has picked up or otherwise 
acquired a character that belongs to another race and not to 
his own. All his achievements, all his capacities, are within 
the limits of his racial characters and the conditions controlling 
their development. 

The individual is in actual possession of all the characters of 
the race. That this is true is shown by breeding experiences 
everywhere, for in all cases the individual transmits to some 
degree all the characters of his race. Milk secretion is a char- 
acter limited to mammals and functional only in the female sex, 
yet every dairyman knows that the bull will transmit milking 
qualities as successfully as will the cow. 

Our experience with reversions — those "long-lost charac- 
ters " that return to plague us — is convincing proof of the fact 
that every character of the race is potentially present in every 
individual, whether the degree of development be much or little. 
In no other manner could they be so long and so persistently 
preserved in the race. Their repeated appearance, long after 
they have ceased to be typical, only shows that they were never 
truly lost. 

The individual is, therefore, born with all the possibilities of 
the race to which he belongs. Those which shall develop and 
fix the type will depend upon two considerations, — first, the 



TRANSMISSION OF MODIFICATIONS 36 1 

relative intensity of their inheritance, and second, the opportun- 
ities for their development. 

The achievements of a race under one environment, therefore, 
cannot be considered as limiting, or even very closely indicating, 
its possibilities under another, and we never know the possibili- 
ties of a race until we have seen it bred and reared under a 
great variety of conditions, — all of which is but another way 
of saying that vastly more is present and transmitted than even 
keen observers are aware of. Everything that belongs to the 
race is always present and is always transmitted in some degree. 
It is sheer business folly, as well as bad science, to conceive of 
characters as being lost for generations, then appearing again. 

Whatever the individual comes to be, therefore, in his adult 
state, he is to be regarded as the irpository of all the charac- 
ters of his race, only a few of which have reached anything 
like their highest possible development in his particular per- 
sonality, and many of which remain so undeveloped as to be 
unnoticed perhaps throughout his entire lifetime. That they are 
potentially present, however, is attested by his descendants. 

Highly differentiated races are so rich in possibilities and so 
great in their range of characters, that the lifetime of any indi- 
vidual is too short, and his environment too circumscribed, to 
realize more than a fraction of his possibilities ; but he transmits 
the remainder as an undeveloped heritage to his descendants. 
WJiat noiu, if any, is the effect npon transmission, of the partic2ilar 
development that he has realiced in his ozvji personality ? Will 
the special cJiaracters that he has strojigly developed be transmitted 
with increased intensity because of their recent extreme develop- 
ment^ or will this development have no effect npon their initial 
powers in the next generations ? This is the one question we 
repeatedly ask ourselves, for it is the one we most desire to 
answer. 

Degree of development depends upon both germinal and environ- 
mental influences. The evolution of a mature and adult individual 
from a fertilized germ is to be regarded as essentially a process 
of development. It has been shown that all differences between 
adult individuals of the same race are due to the degree of 
development which the racial characters have been able to attain. 



362 TRANSMISSION 

This, and not the introduction of new characters, is the basis 
of variation between individuals of the same race. Differences 
between races may be either quahtative or quantitative, or 
both ; but differences between individuals of the same race are 
essentially quantitative. 

Quantitatively, that which is transmitted from parent to off- 
spring is a certain capacity for development. But possession 
of the capacity for development is no guaranty that development 
will follow. Whether or not it will follow depends upon the 
nature of the conditions of life, and whether they will afford the 
opportunity for development. 

The limits of development of any racial character are fixed, 
therefore, by two factors : first, the initial impulse born into the 
individual, the intensity of which is a matter of breeding ; and 
second, the attitude of the environment, whether favorable or 
unfavorable. 

Manifestly with any individual the highest development will 
be in those characters whose inherited intensity is strongest and 
for whose development the environment is most favorable. Next 
in order will come those with high intensity but which are forced 
to struggle against an unfavorable environment, as well as those 
whose inherited intensity is less. Weakest of all will be the de- 
velopment of those characters whose inherited intensity is low and 
for which the environment is especially unfavorable. As we have 
seen, no matter what may be the environment, no development 
will take place except along lines that are clearly recognized 
as within racial possibilities and therefore due to transmitted 
impulses. These contingencies cover all cases of variation 
between individuals, and the real question before the student 
is not whether acquired characters are inherited, but it is this : 
Will the extreme development of a racial character under unusu- 
ally favorable conditions of life augment even to the slightest 
degree the transviittcd tendency for development in the next gen- 
eration ? or are intensities the product only of changes internal 
to the germ plasm } 

Stated more broadly the question is this : Does the develop- 
ment attained by the individual influence his powers of transmis- 
sion .'' This question should stand out clear-cut in the student's 



TRANSMISSION OF MODIFICATIONS 363 

mind. It is not whether an individual with strong tendencies is 
a better breeder than one with weaker tendencies, — that is 
conceded; it is not whether a race Hving under a favorable 
environment flourishes better than one living under hard con- 
ditions, — that is conceded, too, for natural selection is inevi- 
table ; but the question is, whether the individual will be the 
better or the worse as a breeder because of the special develop- 
ment he has acquired. 

The answer to this will decide the question whether we shall 
keep our meat-breeding animals in high or in moderate flesh ; 
whether we must develop the speed of our racing stallions and 
mares ; whether a given sire or dam is a better breeder after 
speed is developed than was the same individual when green. 
It will determine the whole matter of the importance of develop- 
ing breeding stock, not only as a means of increasing natural 
capacity, but as a means of intensifying the powers of trans- 
mission. 

Fortunately we are not without facts bearing upon this 
vexed question ; but the whole field is exceedingly difficult, and 
reliable evidence is eagerly sought. It is the more difficult to 
secure because of the ever-present and always powerful influence 
of selection. 

The particular modifications (acquired characters) that have 
been most discussed and whose transmissibility has been advo- 
cated on the one hand or denied upon the other are of four 
distinct kinds : 

1. Mutilations due to injury or destruction of racial characters 
after they have reached full development. 

2. Habits of life arising out of the exigencies of existence. 

3. Structural peculiarities due to use and disuse. 

4. Adaptations to climatic conditions. 

These are commonly all considered as acquisitions in the 
sense of additions to racial characteristics. In the view advo- 
cated by the writer they are all reducible either to different 
degrees of development of racial characters, or to the uses to 
which these are put under the conditions and exigencies of 
life. They will be considered in the order named, always with 
the question uppermost in mind, Are they transmissible .'' 



364 TRANSMISSION' 

SECTION III — EVIDENCE FROM MUTILATIONS 

Mutilation is the forcible removal of a part after it has de- 
veloped, or at least the destruction of those parts which are fully 
endowed with the power of complete development. Unfortu- 
nately, in this field the most absurd stories have gained credence, 
and their popular acceptance has done much to obscure the 
whole subject. Some one owned a cat whose tail was pinched 
off in a door, and straightway all her kittens were tailless. A 
few semi-traditional stories like this are made the foundation for 
believing in the transmission of mutilations, the facts being for- 
gotten that for generations it has been the custom to remove 
the tails from lambs, with no sign yet of tailless sheep as a 
result, and that circumcision has been practiced by many tribes 
from the remotest times, and by the Jews certainly for four 
thousand years, apparently without effect upon the natural de- 
velopment of parts. Certainly, if any effect has been produced, 
it is not evident, and is so small as to be classed among negli- 
gible quantities, falling entirely outside the field of practical 
results. 

The tail, being a portion of the vertebral column, might be 
expected to long resist all influences toward its suppression ; 
but the prepuce is an unimportant and recent structural addi- 
tion, yet still it lingers, despite persistent and systematic 
removal by force. 

The question lies deeper than the surface. A mutilation, like 
any other difference, in order to be transmitted, must first 
effect the germ plasm, which is the only material carried over. 
If Darwin's theory of gemmules were true, then it might be con- 
ceivable that a defective part would no longer produce its share 
of the germ plasm, and that it would certainly disappear from 
the race, and that at once. The fact that persistently mutilated 
parts do not disappear is good proof not only that mutilations 
are not transmitted, but that the theory of gemmules is incorrect. 

For the most part, belief in the inheritance of mutilation has 
rested, not upon experimental evidence, but upon instances in 
which natural deformities in the offspring correspond to muti- 
lations in the parents. Such correspondence is assumed to be 



TRANSMISSION OF MODIFICATIONS 365 

proof of a causative relation, so quick are we to accept for fact 
that which is not only plausible but startling. In this way a 
mass of evidence (?) has accumulated on this subject second in 
amount only to that bearing upon birthmarks and upon the 
" control of sex." 

The law of chance. Before subjects of this character can 
be properly studied, the operations of the mathematical law of 
chance must be comprehended and their effects deducted. 

If we toss a coin the odds are even that " heads " will be up ; 
they are also even for " tails up." There being but one alterna- 
tive, either heads or tails is certain to appear. When the ne.xt 
toss is made the odds are again even, but there is no causative 
relation between the first and second events. They may agree 
or they may differ ; that is, both may be heads, both may be 
tails, or one may be heads and the other tails. 

Successive tosses will give rise to an extremely irregular 
series, as may be shown by trial. However, if the series be 
continued indefinitely and tally be kept, it will be found that in 
the long run the heads and the tails ivill be equal. When the 
equality will first occur is entirely uncertain. It may be at the 
second throw or it may be at the hundredth, or even later, but 
it is certain to come. 

The roulette wheel, as commonly used, is made up of thirty- 
seven color spaces, eighteen red and nineteen black, or the 
reverse. The wager is laid upon the number or the color on 
which the wheel will rest after a supposedly impartial spin. It is 
evident that the probability of its resting upon a particular num- 
ber is but one in thirty-seven if the wheel is mechanically per- 
fect, and that the chances of its resting upon a particular color 
are not quite even. This difference of nineteen to eighteen 
constitutes the "advantage" of the owner over the player, and 
shows the hopelessness of attempting to " break the bank." 
This margin of one out of every thirty-seven bets is over 2.5 
per cent of the business and constitutes the assured profit in a 
game of chance conducted honestly on this plan, — which is 
the one in use at Monte Carlo, the greatest gambling house in 
the world. 1 

^ See Pearson, Chances of Death, pp. 42-62. 



366 TRANSMISSION 

The successions of red and black representing gain and loss 
are so irregular and so confusing that the player fails to detect 
the ratio of more than 5 per cent that is against him, and con- 
sequently does not realize that the longer he plays the more 
certain are his losses. Nor does he realize that in the long run 
nothing is more absolutely certain than the law of chance. The 
deviation is not great at any point after the first few throws, 
and herein lies the first deceptive quality of all games of chance. 

If the letters of the word "incomprehensibility" be tossed 
into the air in such a manner that they must fall into a line, the 
chances of their falling in the proper order to spell the word 
correctly are exceedingly remote, yet it is bound to happen if the 
trials are long enough continued. 

These simple facts teach us not to attach too much impor- 
tance to occasional occurrences, however strange or apparently 
improbable. They teach us, too, that there may be no special 
cause at the bottom of the occurrence beyond the mathematical 
law of probability. The tossing of coins shows why it is, for 
example, that every theory for the control of sex that ever has 
been or ever can be invented has been repeatedly verified. 
There is but one alternative, and every assumption of cause, 
however absurd, is certain to come true (.'') half the time, which 
is sufificient proof for most people who depend upon memory 
impressions rather than upon absolute records. 

Proof by the method of instance is therefore extremely 
hazardous. Something more than the mere fact of coincidence 
is necessary in order to establish a causative relation with any 
very high degree of certainty. 

When, therefore, a deformity in a child corresponds to a muti- 
lation in a parent we are not warranted in at once assuming a 
causative relation. We are to remember that deformities of all 
kinds are comparatively common; that mutilations are exceed- 
ingly so ; that frequently a mutilation will resemble a natural 
deformity or an injury ; and that occasionally, under the laws of 
probability, the mutilation of the parent will resemble the 
deformity in the offspring, thus suggesting direct transmission. 
We are to remember, too, that the law of chance must first be 
satisfied before we can assume causation. 



TRANSMISSION OF MODIFICATIONS 367 

The most direct way of procedure is, however, not to endeavor 
to ehminate the law of chance, but, by direct experiment, 
to learn whether a sufficient number of occurrences can be 
established to clearly exceed in number any possible coincidence. 

Experimental evidence on inheritance of mutilations. The 
facts just given show conclusively the hazard of framing theories 
on chance occurrences, and demonstrate the practical worthless- 
ness of all but experimental evidence in the study of inheritance. 

Unfortunately but little evidence of this kind is at hand, and, 
so far as is known to the writer, that which is at hand is confined 
to artificial injuries to the nerve, with exception of that already 
cited in such practices as docking and circumcision. 

Romanes outlines seven classes of abnormalities that appeared 
in the offspring of guinea pigs corresponding to those artificially 
produced in the parents by Brown-Sequard and his assistants. 
They are in brief as follows : ^ 

1. Appearance of epilepsy, when parents have been rendered 
epileptic by an injury to the spinal cord. 

2. Same, when the injury had been to the sciatic nerve. 

3. Change in the shape of ear in animals born of parents in 
which such a change was the effect of a division of the cervical 
sympathetic nerve. 

4. Partial closure of the eyelids in young born of parents in 
which that state of the eyelids had been induced by section of 
the cervical sympathetic nerve or the removal of the superior 
cervical ganglion. 

5. Exophthalmia in young born of parents in which a similar 
protrusion of the eyeball had been produced by injury to the 
restiform body. 

6. Gangrene of the ears in animals whose parents' ears had 
been affected by injury to the restiform body. 

7. Absence of toes in young whose parents had eaten off 
their toes, which had become "anaesthetic" by reason of the 
section of the sciatic nerve alone or of that nerve and the crural. 

8. Various morbid states of the skin and hair corresponding 
to a similar condition of the parents which had been brought on 
by an injury to the sciatic nerve. 

^ Romanes, Darwin and After Danvin, II, 103-122. 



368 



TRANSMISSION 



It is notable that all these experiments are based upon injury 
to the nerve and are of a degree of severity likely to affect the 
entire organism seriously. If, however, it is true that injury of 
any kind in the parent leads, as Brown-Sequard and Romanes 
evidently suppose, to corresponding deformities in the offspring, 
the fact is exceedingly significant. This is a field, however, 
quite different from that of ordinary injuries — such as the 
removal of a horn or a tail, producing no constitutional disturb- 
ance and leading to no organic changes. Further experiments 
are greatly needed to confirm, deny, or modify the results of 
Brown-Sequard. In the meantime it seems almost incredible 
that so much erroneous tradition should have grown up sur- 
rounding this matter of inherited mutilations, especially when 
the world for unknown generations has almost invariably seen 
perfect children born from one-armed, one-legged, and otherwise 
mutilated parents. Indeed, if offspring inherited the ordinary 
mutilations of their parents, the world would have become long 
since a collectioa of monstrosities which would put to shame the 
rare specimens now collected in dime museums. 

Inheritance of disease. The old tradition of inheritance of dis- 
ease is long since disproved, and those diseases once thought 
to be inherited are now known to arise not from inheritance 
but from infection after birth, which for obvious reasons is ex- 
tremely easy between parent and offspring. 

The weakening effect of wasting diseases upon the parents, 
and the influence of this weakening upon the constitution of the 
offspring, inducing predisposition to disease, is, however, quite 
another matter. That many of the effects of such a disease of 
the parents will work injury and weakness to the offspring will 
be readily admitted ; that such offspring will be the more sus- 
ceptible to attack from diseases of all kinds will hardly be 
denied ; but whether it will be peculiarly susceptible to the spe- 
cial disease that zvrought havoc zvith the parent is a question 
on which we need much more evidence. 

Up to date this point has not, in the opinion of the writer, 
been established. Although it is true that certain family lines 
are specially susceptible to tuberculosis, it is not yet shown 
whether this susceptibility is the result of inroads of this special 



TRANSMISSION OF MODIFICATIONS 369 

disease or whether it is caused by weakness in family Unes des- 
tined to disappear, and for whose extinction tuberculosis is the 
special agent of natural selection. The weight of evidence inclines 
the writer to a belief in progressive immunity from diseases of this 
class, — a matter touched upon under the subject of acclimati- 
zation. That the spavined mare will not transmit her spavin is 
as fortunate as it is true, but the question lying back of this 
fact is, Why was she spavined ? Is the injury an evidence of 
weakness, or is it only the result of an accident, such as might 
have happened to any horse .-' If it is the former, then the 
weakness, not the spavin, will be transmitted ; if it is the latter, 
there is in all probability not the slightest danger. If injuries of 
this sort were transmissible, our horses would long since have 
acquired a collection of spavins, ringbones, splints, sidebones, 
and curbs such that no leg could hold them. It is far from the 
purpose of the writer to advocate the use of defectives as 
breeders, but we cannot close our eyes to the fact that a mare 
which has seen hard service and bears the marks of it is in all 
likelihood a better breeder than another that has never been put 
to the test, no matter how clean and free from blemishes the 
limbs of the latter may be. The stubborn fact is that the risk 
of accident is so great that a horse put to hard service is certain 
to be blemished sometime ; and so far as present knowledge goes, 
she is as good a breeder after the accident as she was before, — 
which is far from saying that every blemished horse is fit for 
breeding purposes. 

The writer is clearly of the opinion that, even with the ex- 
periments of Brown-Sequard in mind, the evidence warrants 
the conclusion that ordinary injuries to the body are not trans- 
mitted to the offspring. Whether different results follow those 
profound injuries that reach the nerve centers and work con- 
stitutional changes in the organism is a matter on which we 
must await further evidence. 

Mutilations have reference to characters already fully devel- 
oped, and therefore fully provided for in the germinal matter. 
If violent removal is to lead to their suppression, it must lead to 
it through some sort of retroactive influence affecting the germ 
in exactly the proper particular and no other, — a presvmiption 



370 



TRANSMISSION- 



that is inconceivable under any law of physiology that is known 
or that can be imagined. 

The non-development of parts is another and quite a different 
matter. If the non-development be due to a defective germ, it 
of course does not come under the present inquiry. If, however, 
it be due to an injury at an early stage, resulting in arrested 
development, it may or may not be equivalent to a mutilation. 
If the non-development be due to the destruction of cells, as 
in chemical dehorning, it is to all intents and purposes a mutila- 
tion, as conditions were present for full development. If the 
non-development be due to malnutrition, the case is different, 
and belongs among cases to be considered later. 

The essential weakness of the whole theory that mutilations 
may be transmitted lies in the fact that the characters in question 
are present, fully developed and functional, until removed by vio- 
lence, all of which is conclusive evidence of a natural capacity 
for complete development. In view of our inability to conceive 
how the removal of a part can possibly affect the corresponding 
portion of an undeveloped and even unfertilized germ ; in the 
absence of reliable experimental data and with the certainty that, 
were the injuries due to the multitude of accidents occurring to 
all forms of life transmitted all species would soon be disfigured 
by an overwhelming mass of inherited mutilations, — in view of 
all these facts we are certainly warranted in feeling assured that 
injuries to the fully developed body are not transmitted. 

SECTION IV — EVIDENCE FROM FOOD SUPPLY 

This is a very different matter from mutilation. Of all the 
conditions of life this is, par excellence, the limiting element, not 
only in body building and in functional activity, but in constitu- 
tional vigor as well. 

That the amount of food available is a controlling factor in 
the development of size is a matter too well known to require 
discussion. In the presence of abundant food, animals and plants 
of all species attain their maximum size and their maximum 
development in all respects. If the supply be limited, the effect 
is invariably seen in under-development, even though the total 



TRANSMISSION OF MODIFICATIONS 371 

amount consumed is many times greater than that actually used 
in body building. 

In acclimating to a shortened food supply the animal or plant 
is forced, not so much to make more economical use of what it 
can obtain as to reduce the scale of living and actually to accom- 
plish less in the way of growth and functional activity generally. 
A starving animal or plant will make the most of all available 
food, but in addition the animal will replace a large share of the 
dry matter of the body with water and reduce its activity to a 
minimum before it succumbs, and a starving plant will still put 
forth new leaves, using the substance of the old to nourish 
the new. 

If the shortage in food comes before development is complete 
its effect is seen in under-development, or possibly in arrested 
development, — recognized by the farmer under the term 
" stunted." Sometimes the condition is only temporary, but 
more often it is permanent, when no amount of food later in life 
will avail to repair the damage done by shortage during devel- 
opment. Farmers accordingly recognize the period of growth 
as a "critical period," and uniformly say that if any live stock 
is to be short of feed let it be the older ones. Sad experience 
has taught the irreparable evil of shortage in food during 
development. 

Under-nourishment strikes at the very root of life as well as 
at development. What is true of individuals seems true of 
races. Under-nourishment is followed by a lowering of tone 
and a lessened rate of living, while full feed and maximum con- 
ditions of life generally induce great protoplasmic activity and 
rapid cell division, resulting in maximum size and maximum 
functional activity in all parts of the structure. 

All experience goes to show that weakened parents, plant or 
animal, give rise to young that are low in vigor and slow of 
growth. Seed corn that is below the normal in vitality, though 
it may germinate, will give rise to weak and slow-growing plants. 

There are all degrees of vigor and intensity of the vital 
processes, from zero up, and nothing seems more potent than 
the food supply in influencing this matter that lies at the basis 
of all development and all functional activity. 



372 



TRANSMISSION 



As temperature is an all-pervading influence with smaller 
organisms, so is food an all-pervading influence with all organ- 
isms, large or small. Without doubt it exerts a controlling effect 
upon the quality of germinal matter produced, as it does upon 
its quantity, and upon the maximum or minimum development 
of the body. 

Constitutional vigor, which is the most valuable asset of any 
plant or animal, is a heritage whose seat is in the germ from 
which it was developed. Such a germ could be produced only 
by a vigorous, healthy, well-nourished parent. Anything which 
weakens this parent constitutionally, which lowers its tone, 
reduces its vital powers, and lowers its rate of living, must 
of necessity affect the quality of any germinal matter it may 
produce and the constitutional vigor of its descendants. 

We do not permit this condition to any large extent in our 
domesticated species, plant or animal, for we realize too well 
the consequences, but we have only to look among the underfed 
classes and races of humans to see the evil effects of malnutri- 
tion in weakened constitutions, low vitality, predisposition to the 
ravages of disease, and general inefficiency wherever any great 
functional activity, physical or mental, is required. That this 
condition is transmitted does not admit of a reasonable doubt. 

On the other hand, races that are well nourished for many 
generations undergo maximum development. This has been the 
experience with all domesticated animals and plants. For the 
most part they have been provided with all the food they needed, 
and they have responded with a development such as never 
came to them under natural conditions. 

Nature never produced such specimens as our modern beef 
or milk breeds or our draft horses. Our achievement as breed- 
ers is due, therefore, to something besides selection, and we are 
forced to one of three conclusions : 

1. That nature never produced a perfect specimen ; that is, 
that natural conditions were never sufficiently favorable to allow 
the individual to realize the full development to which his natural 
endowments entitled him. 

2. That with each increment of gain through selection, estab- 
lishing a higher general average, a new " center of variation " 



TRANSMISSION OF MODIFICATIONS 373 

was also established, which was bound in time to produce better 
specimens than ever before. 

3. That there has been direct transmission of the increased 
vigor and powers of nutrition and growth that come from full 
feed. 

The first conclusion is unthinkable. Nature must certainly 
have produced, occasionally at least, perfect specimens of their 
kind, and the belief that this is so is favored by the fact that 
wild things do not respond generously to full feed. 

The second is without doubt a real fact in evolution, difficult 
as it is to comprehend. Later, in statistical studies, it will be 
found to our satisfaction that as the average is raised by selec- 
tion ncii' values appear at tJie top, — a fact on which depends, 
without doubt, a large share of our improvement of all species. 

And yet we cannot fight off the conviction that here, at this 
point, lying so close to the very springs of life, the absolute con- 
dition of life — nutrition — exerts a controlling influence upon 
that mysterious force which we call the vital principle, and whose 
relative strength we measure by such terms as "constitution" 
and "vigor." That vigor, or the lack of it, is a transmissible 
character no one will deny, or even doubt ; and it is the firm 
conviction of the writer that when this vigor, or scale of living, 
has been strengthened or weakened from any cause, the power 
of the individual to transmit a vigorous constitution to its off- 
spring will be enhanced or lessened accordingly, and that when 
the last word shall have been spoken upon the disputed ques- 
tion of inheritance or non-inheritance of acquired characters it 
will be found to square with this fact. 

The writer desires, above all things, not to dogmatize. Facts, 
not opinions, are needed in these uncertain fields ; and yet, until 
the partisan advocates of the opposite sides of this question will 
divide the question and discuss separately the three or four dis- 
tinctly different issues involved, — until that time, practical 
breeders must not be deceived or lulled into carelessness by the 
dictum that " acquired characters are not transmitted." 

Increased development above the natural in one form or 
another is the principal object in all improvement, and a large 
share of the possibility of such increased development lies in 



374 



TRANSMISSION 



this matter of constitutional vigor, which so largely depends 
upon nutrition that the breeder can afford to make no mistake 
at this point. 

Influences that strike at the root of the vital principle, what- 
ever that may be, are far reaching in their consequences. To 
maintain the vital powers at a maximum is one of the prime 
objects in all breeding, and that this is to a large extent a 
matter of nutrition is a fact that should be fully appreciated 
by him who hopes to maintain unimpaired the valuable racial 
characters for which he breeds his animals and his plants. 

There is no better maxim for the breeder than this : the 
results of good feed are transmitted to the offspring in the form 
of a vigorous constitution and large powers of assimilation and 
of service. 

SECTION V — EVIDENCE FROM ACCLIMATIZATION 

It is a well-known fact that the individual acquires by experi- 
ence a high degree of resistance to temperature, poisons, or 
other adverse conditions of life ; that this modification is more 
or less permanent with the individual and that in good time the 
race as a ivJiolc becomes acclimatized to changed but persistent 
conditions.^ Is this race acclimatization in any way the result 
of transmission of the acclimatization of the individual ? 

1 It should be clearly understood that " acclimatization " is not confined to 
adverse conditions ; it may relate as well to adaptation to improved conditions, 
such as increased food supply. Indeed, the term is intended to cover accoiiuno- 
dation to any change iii exte7-nal coiditious of life, whether favorable or unfavorable, 
gradual or sudden. 

As is well known, acclimatization is more successful if the subjection be 
gradual ; but, in any event, one of two results will follow if the individual is not 
killed in the process: (i) it will become permanently altered, and will therefore 
discharge its functions in a modified manner; or (2) it will acquire by experience 
so high a degree of resistance as to be able to resume its usual activities after 
the first disturbance and afterward to discharge its normal functions in spite of 
adverse conditions. 

There are thus two kinds of acclimatization : one in which the functions or 
activities are modified, the other in which the individual succeeds in resisting the 
changed conditions, and therefore in preserving its normal functions. Of the 
two, the latter is perhaps the more common. The former betrays the more con- 
stitutional change, the latter the greater elasticity in organization. 



TRANSMISSION OF MODIFICATIONS 375 

To determine whether in the acclimatization of a race agen- 
cies are involved other than selection operating upon individuals, 
it is necessary either to eliminate the results due to selection or 
else to discover cases in which it does not occur. While the 
first is all but impossible of accomplishment with any feeling of 
assurance, the second is, in the opinion of the writer, entirely 
feasible, especially in certain lines. 

The importance of the whole question and the difficulty of 
securing reliable data are sufficient excuse for introducing a 
somewhat full discussion of certain topics which afford evidence 
upon the question at hand. 

Extent of acclimatization. The power of the individual to 
adapt itself to changed conditions is something marvelous, as 
has been seen under the subject of causes of variation and in the 
discussion of relative stability. This same elasticity of organi- 
zation is characteristic of races as a whole. By means of this 
adaptability many species of both animals and plants have 
totally changed their habitat, and with this -change have under- 
gone the most sweeping alterations. The whale is developed 
from a land mammal and is suffering degeneracy as a conse- 
quence. Swine have been adapted from a diet of roots and 
flesh to one mainly of grain. Horses and cattle in their wild 
state subsisted entirely on pasture, but with us their diet is 
from 25 to 75 per cent grain. Sheep are mountain animals, but 
they have been adapted to the richest pastures and the lowest 
plains. The turkey, native to North America, is making his 
way over all the earth, as chickens have scattered broadcast 
from their native habitat in southeastern Asia. 

The potato, native to the mountains of Peru, is now grown 
everywhere in temperate regions, though it never succeeded in 
acclimating in the tropics except in high altitudes. There are 
evident limits, or else the possibilities are not yet exhausted. 

Corn (maize) will endure but slight change in locality without 
suffering seriously, yet after a few years it appears to recover 
tone and succeed. In this way the culture of this crop has been 
gradually moving northward in the United States, until now it 
is fully acclimated in regions in which a quarter of a century ago 
its culture was impossible. So sensitive is the corn plant to 



376 TRANSMISSION" 

climatic change, but so readily does it adjust itself, that new 
varieties can be introduced successfully, provided they are given 
considerable time to acclimate on a small scale before their pro- 
duction under field conditions is attempted. 

Wheat has extended almost over the earth, except in extreme 
latitudes. The varieties have become so well fixed in the various 
regions that when brought from long distances they seldom thrive 
at first. Some strains never succeed, but others acclimate per- 
fectly in new localities. Varieties may be changed readily from 
spring to winter sorts, and the hibernating habit become fixed, 
as in other biennials. 

Imported animals are seldom fertile until acclimated. It is 
said, however, that certain breeds of the dog never acclimate in 
India sufficiently well to preserve their distinctive racial charac- 
ters. On the other hand, species occasionally prosper better in 
new localities than in old ones. Generally speaking, distance 
makes less difference than altitude, temperature, sunlight, and 
food supply. The evident principle involved is the influence, 
favorable or otherwise, of certain elements of climate upon the 
development of racial characters. 

Acclimatization to temperatures. It is a well-known fact that 
if we bring together and put under the same conditions plants 
or cuttings of the same species but grown in different latitudes 
or altitudes, and therefore habitually exposed to widely different 
temperatures, those from the more northern localities and the 
higher altitudes will be the first to put out bud and leaf. 

De Candolle of Switzerland, and Bailey of New York, have 
both conducted extensive experiments in this direction, and with 
the same results. ^ 

The former took, among others, cuttings of the poplar, the 
tulip tree, and the catalpa, both from Montpellier and from 
Geneva, and planted them at the latter place in glasses of water 
with sand at the bottom. In every case those taken from 
Geneva, the colder locality, leafed out first. The difference in 
the case of the poplar was about twenty-three days, in the case 
of the tulip tree about eighteen days, and in the case of the 
catalpa twenty days. 

1 Bailey, Survival of the Unlike, pp. 296-301. 



TRANSMISSION OF MODIFICATIONS 



377 



Montpellier is situated in southern France on the Mediter- 
ranean, within a few miles of the coast ; Geneva is at the head 
of Lake Geneva in Switzerland. The two points are, therefore, 
separated by about two and a half degrees of latitude, with a 
difference of about twelve hundred feet in altitude, and with 
some possible differences in humidity. The main difference, 
however, is one of temperature ; and although both the tulip tree 
and the catalpa had been originally introduced from America, 
they had evidently become so physiologically modified by their 
new surroundings as to exhibit substantial diversity in their 
reactions to the same temperatures. 

Bailey found that cuttings of Lombardy poplar from northern 
Maine unfolded their buds two days earlier than similar cuttings 
taken at Ithaca. He placed under the same conditions cuttings 
of the Concord grape taken from Maine, New York, and southern 
Louisiana, and found that they leafed out in the order of their 
locality, beginning with the most northerly. He reports similar 
results from potatoes. 

These were cuttings, and the experiments show that the indi- 
vidual plants from which they were taken had become thoroughly 
acclimated. Whether any selection had been involved in this 
acclimatization we do not know, and we cannot tell, or even infer, 
from these experiments whether or not the seeds grown from 
these plants would have behaved in the same way. What is 
shown is that the individual plants were so thoroughly acclimated 
as not to respond in the same degree to identical temperature 
conditions. 

The same behavior has been shown, however, with all seeds 
that have been tried. Bailey found that corn (maize) grown in 
New York germinated more readily than that grown in South 
Carohna or (as shown by the following table) than that grown 
in Alabama : 





Fifth Day 


Sixth Day 


Seventh Day 


Final Total 


New York .... 
Alabama 


14 kernels 
kernels 


33 kernels 

34 kernels 


2 kernels 
5 kernels 


98 per cent 
80 per cent 



Z7^ 



TRANSMISSION 



The corn from New York was evidently the better seed, 
because its final percentage of germination was higher. 

This fact might account for some portion of the difference in 
promptness of germination, but we are informed that during the 
entire month of the experiment the plants from the northern- 
grown seed were the " largest and most vigorous of any." They 
were evidently ahead in their development. Bailey remarks that 
not only "corn gave the most marked results in favor of the 
northern samples, but there was generally a similar difference 
in the watermelons and beans, with not one contrary result." 

Bonnier ^ made observations with Teiicrmm Scorodonia (wood 
sage) for eight years. When grown on the high altitudes of the 
Pyrenees it produced shorter stems, darker-green and more hairy 
leaves, and more compact inflorescence than when grown on lower 
land. Seeds gathered from these plants and sown in Paris, after 
three years in the new habitat "produced elongated stems, with 
less hairy and brighter-green leaves, or plants very similar to 
those from seeds obtained in the neighborhood of Paris." 

The same experimenter collected specimens of other species, 
both in alpine and in arctic regions, and found that those of the 
latter region had "more rounded cells" and larger intercellular 
spaces.^ 

That races as well as individuals acclimate to temperature is 
easily shown and well known, but as the process is generally 
accompanied by selection there is difficulty in finding instances 
free from its influence, and it is practically impossible to assess 
and deduct its results. It is not impossible, however, to find 
cases fairly satisfactory. 

The origin and history of the Shetland pony is not known, 
and yet it is practically certain that its small size is partly the 
result of a cold climate and scanty feed. Under these adverse 
conditions there must have been vigorous natural selection. We 
shall learn in the chapter on " Heredity " that this small size 
could doubtless be accounted for by progressive selection, but 
the question here is whether progressive acclimatization is not 
also involved. 

1 Vernon, Variation in Animals and Plants, p. 312, from which the account 
is taken. ^ Ibid. p. 313. 



TRANSMISSION OF MODIFICATIONS 379 

All things considered, the conviction is forced upon us that 
the Shetlands suffered a progressive diminution because of low 
temperatures or short feed, or both, or else that these northern 
forms, living under hard conditions, lagged behind their more 
fortunate neighbors in the general increase in size that has 
attended the evolution of the horse kind generally. 

The temperature of hot springs varies all the way from 50° to 
98° C.^ So far as known they are all inhabited by living organ- 
isms. The protoplasm of ordinary plants and animals cannot en- 
dure a temperature above 45°. Death quickly follows the attempt 
to raise it much above this point, and the nearest relatives of 
these hot-springs species are no exception to the general rule. 

Yet the fact remains that the hot springs are inhabited, and 
by creatures so small that their temperature must be the same 
as that of the waters in which they hve. How have these waters 
become peopled with organisms living in temperatures ten to 
fifty degrees higher than could be endured by the stock from 
which they must have descended ? ^ 

No amount of selection could account for the fact, for there 
are no other known species living in an environment approach- 
ing these temperatures. There must have been progressive de- 
velopment of some fashion and from some cause. 

Upon this point the experiment of Dalhnger is both signifi- 
cant and valuable.^ He reared Flagellata in an oven where 
control of temperature was absolute. Beginning at 15.6° C, 
he took four months in which to raise the temperature through 
5.5°, a precaution now known to be unnecessary, as Flagellata 
will endure a quick rise to 21°. 

When the temperature reached 23° the organisms " began 
dying, but soon ceased, and after two months the temperature 
was raised half a degree more." After a time it reached 25.5°, 
when they again began to die, and for eight months the temper- 
ature could not be raised even a quarter of a degree above this 

1 C. B. Davenport, Experimental Morphology, Part I, pp. 250-251. 

2 The temperature varies slightly in different parts of hot springs, being lower 
near the edge. 

3 C. B. Davenport, Experimental Morphology, Part I, pp. 252-254; Vernon, 
Variation in Animals and Plants, pp. 379-380; Journal of the Royal Microscopical 
Society, VII, 191. 



38o 



TRANSMISSION 



point. It seemed at this time that a "stationary point" had 
been reached, but ultimately Dallinger was able to make slight 
additions to the temperature, and, " proceeding by slow stages" 
and for "several years," he succeeded at last in reaching 70°, 
when the experiment was terminated by an accident. 

The exact length of time employed in this experiment is not 
stated, but it is supposed by Vernon to be approximately six 
years. Thus these organisms were bred for many generations 
during the experiment, and it is really a case of race acclimati- 
zation. The organisms were monads, it is true, which multiply 
by fission, so that, as Davenport states, " the high temperatures 
acted upon the same protoplasm at the end of the experiment 
as at the beginning." Is there any reasonable doubt that this 
is the process by which organisms of this character have gained 
access to our hot springs even under natural conditions ? 

In this experiment three points are noteworthy : 

1. There were certain "sticking points," so to speak, that 
were difficult to get over, but after these were passed, additional 
increase of heat was easily endured. The temperature of 25.5° 
was one of these sticking points. 

2. It was found that the process of acclimatization did not 
become gradually slower and more difficult with the higher tem- 
peratures, for 25.5° was the most difficult temperature encoun- 
tered, requiring eight months to surmount, while the rise from 
41.7° to 58.3° was made in seven months, and that from 61.1° 
to 70° in a few months (number not stated),^ showing that the 
limits of variability were not reached, and suggesting that the 
experiment might have been continued much longer and the in- 
crease pushed much farther. 

3. Organisms acclimated to 70° died off when returned to the 
original temperature of 15.6°, showing that the modification of 
the protoplasm was not only profound but also permanent. In 
other words, here is a species whose temperature has been 
raised through so many degrees, and its protoplasm so altered, 
that it can no longer endure its original normal temperature. 
It has been taken entirely out of its field and placed in another 
so far removed as to have no connection with its former state. 

1 Vernon, Variation in Animals and Plants, p. 380. 



TRANSMISSION OF MODIFICATIONS 38 1 

It is true there were deaths during this process, but the 
selection tvas insignificant, and the conviction is absolute that 
the result was in no large sense due to the selective process. 

In the opinion of the writer this is proof absolute of one of 
three things : 

1. Either the direct transmission of modifications, — a thing 
not difficult to imagine considering the mild sort of transmission 
involved in reproduction by fission ; 

2. The direct action of the temperature upon the constitu- 
tion of the protoplasmic basis of life, — a contingency not spe- 
cially applicable in this case, where the germ undergoes but 
shght development and there is no practical distinction be- 
tween germ plasm and body plasm ; 

3. Or, if of neither of these, then it is proof of what may 
be called progressive variation, in which, with a species living 
under changing conditions, new centers of variability are being 
constantly established. 

The significant point is that in this instance the deviations 
are due not to selection but to the direct action of the environ- 
ment, and we are left to explain cases of this kind by assuming 
either that the modifications are themselves directly transmitted, 
or else that the external conditions have influenced th-e germ as 
well as the body. 

This is not difficult to believe of such all-pervasive influences 
as temperature, and it may well be that certain outside influences 
can make themselves felt in this way when others w^iich, from 
their nature, may affect the development but cannot reach the 
germ, will not make themselves permanently felt except through 
individual adaptation and selection. 

Acclimatization to poisons. That individuals acquire a high 
resistance to poisons has already been shown. Speaking gener- 
ally, living protoplasm will soon adjust itself to any chemical 
influence not fatal or so extremely injurious as to overcome its 
powers of adaptability. Physicians change remedies frequently 
for the reason that they soon lose their characteristic action. 

The acquired resistance of man to arsenic and other poisons, 
of mice to ricin, of the horse to the filtrate of the diphtheria 
bacillus, of the rabbit to that of hydrophobia, and of animals 



382 TRANSMISSION 

in general to poisons of all sorts gradually administered, is 
well known. ^ 

So far as we are able to judge, immunity to infectious diseases 
is produced in the same way. One attack of certain diseases 
serves to render the individual immune through life. The 
question that interests us at this point is this : Is this immunity 
in any sense, or to any degree, transmitted to the descendants ? 

It is claimed by some that if a sow recovers from a case of 
hog cholera suffered while carrying young, the pigs will be born 
with a high degree of resistance, if not absolute immunity ; the 
idea being that they acquired /;/ titero from the blood serum of 
the mother the same kind of immunity that could be produced 
by inoculation. 

There is too little experimental evidence as yet, and we know 
too little of the real nature of acclimatization, to warrant positive 
conclusions. What is known, however, is sufficient to raise some 
interesting and exceedingly suggestive questions. 

If immunity can be produced in the mother by the repeated 
injection of the chemical products of disease, and if such im- 
munity be permanent, then why should not the young, whose 
blood serum is derived from the mother, be also of the same 
character.? Whence come our "natural immunes " .? are they 
mutants, or are they the products of immunizing influences 
from the parentage ? Recent investigations seem to indicate 
specific qualities in blood serum, '-^ and it may very well be 
that "blood relationship" means more than we have hitherto 
supposed. 

To what extent immunity is purely a chemical question, and 
to what extent it is connected with the power of the white 
corpuscles to attack and digest invading organisms, we do not 
know. In so far as it depends upon or affects the serum of the 
blood it may well be a transmissible quality from the female 
mammal if not from other parents. 

1 C. B. Davenport, Experimental Morphology, Part I, pp. 2S-32 ; Vernon, 
Variation in Animals and Plants, pp. 386-387. 

2 When the blood serum of one species is injected into the veins of another, 
the most injurious effects are said often to follow, and the so-called precipitin 
test seems to establish the fact that differences in blood serum of different species 
are profound. See Blood Immunity and Blood Relationship, by Nuttall, reviewed 
in Science, October 28, 1904. 



TRANSMISSION OF MODIFICATIONS 383 

Chemical action of normal secretions. In the opinion of tlie 
writer, those who discuss the subject of the transmission of 
modifications (acquired characters) as if it were a single issue, 
and cHsmiss it in toto as impossible upon the theoretical ground 
that no such modifications could by any manner of means affect 
the germ plasm — those who discuss and dismiss the matter in 
this manner commit a fundamental error in overlooking the 
fact that, as a whole, this is a broad question, or rather a series 
of questions, and that the living organisms, exposed as they 
are for generations to outside conditions absolutely essential to 
their existence, present many points of contact in which they 
are exceedingly susceptible to influence. They make the fatal 
error, too, of failing to distinguish between those circumstances 
that affect only the externals of the body and those all-pervading 
influences that affect the very constitution of the organism. 

For example, it is now well known that the perfect working 
of the body as a whole depends upon the presence of specific 
secretions of certain organs, many of which were once thought 
to be functionless. Destruction of the thyroid gland at once 
arrests not only the physical but the mental development. In 
children its degeneration results in retarded mental development 
and even in idiocy, a calamity that can be ameliorated, and even 
averted, by the injection of thyroid substance of animals. Bau- 
mann found that the secretions of this gland are characterized by 
the presence of iodin, which is found nowhere else in the body.^ 

On this same general question Vernon, after speaking of the 
frequently fatal effect of removing the thyroid gland, unless the 
animal be fed thyroid substance, remarks as follows :^ 

Extirpation of the suprarenal glands results in much more speedy death, 
and here again the injection of extracts may delay the fatal issue. Extir- 
pation of the pancreas causes the production of severe diabetes, and uhi- 
mately death, but such an effect may be avoided by the grafting of a 
portion of excised gland in the peritoneal cavity or the tissues. . . . Again, 
extirpation of the total kidney substance of the dog leads, not to a dimin- 
ished secretion of urine, but to a largely increased secretion, accompanied 
by a rapid wasting away, which soon ends fatally. Hence the kidneys may 
possess an influence on the metabolism of the whole body, as well as their 

1 I oeb, Physiology of the Brain, pp. 207-20S. Extracts of this and other 
glands are now regularly prepared at our larger slaughterhouses, 

2 Vernon, Variation in Animals and Plants, pp. 358-360. 



384 TRANSMISSION 

obvious secretory function. Tlie spleen appears to have an internal secre- 
tion which is of influence in setting free the pancreatic ferment. Finally, 
extracts of various nervous tissues — -brain, spinal cord, and sciatic nerve — 
have been found, when intravenously injected, to produce a distinct fall of 
blood pressure,^ whilst those of the pituitary body produce a marked rise. 

Here is a basis for possible transmission of such diseases as 
might be connected with normal secretions, as it certainly is for 
any external influence that could permanently affect either their 
character or their quantity. This opens a wide field for the pos- 
sible and permanent influence of causes of variation lying origi- 
nally outside the germ, but whose effects are of such a nature 
as to make themselves felt throughout the entire organism, and 
to influence not only its development and activity but its power 
of transmission as well. 

Akin to this is the possible effect of such chemicals as alco- 
hol, which has specific relations to protoplasm and is one of 
those influences that apparently are capable of penetrating to 
the uttermost limits of the organism. Without doubt other mate- 
rial elements of food and drink exert fundamental influences 
of a chemical nature, whose effects may reach the germinal mat- 
ter and thus of necessity descend from generation to generation, 
to the distinct modification of the race. 

How races acclimate. How do races become acclimated ? 
There are at least five methods competent to explain the 
process : 

1. The accliinatization of all the individuals of a race, each 
one in the successive generations separately ; 

2. Selection, obliterating such individuals as are unable to 
acclimate successfully, thus restricting descent to the fittest ; 

3. The direct transmission of individual modifications (ac- 
quired characters), at least in some slight degree, the accumula- 
tion of which ultimately produces complete acclimatization in 
the race ; 

4. It is possible that the same causes which induce modifica- 
tions in the individuals may also exert influences so deep-seated 
as to affect the germ plasm directly and in this way produce all 
the appearances of inheritance of modification ; 

1 Due probably to specific action on the heart. 



TRANSMISSION OF MODIFICATIONS 385 

5. The process may be explained by the old principle of pro- 
gressive variation. 

Of these, the first two are certainly always at work. Mani- 
festly all the individuals of succeeding generations, or most of 
them at least, will spontaneously acclimate to the changed con- 
dition. This of itself would give an appearance of race acclimati- 
sation, even though no change had been wrought in its inherited 
nature'. If, now, to this is added the effect of selection, we at 
once recognize a powerful cause of real race acclimatization. 
Nor does this necessitate the destruction of any very large 
nvimbers. If only their life period be shortened or their fer- 
tility decreased, their relative importance in the race would be 
greatly lessened thereby and the effect of selection felt. 

Either one of these two processes alone is entirely competent 
to account for the full appearance of acclimatization. Doubtless 
both are always present and at work jointly, but this does not 
preclude the possibility of other agencies also. The fifth possi- 
bility depends upon selection for its efficiency. 

The chief objection to relying upon selection to fully account 
for race acclimatization is that the destruction is frequently too 
slight, and the race response too prompt ; yet it is not sufficiently 
prompt and instantly complete to account for the phenomena by 
the successive acclimatization of all individuals separately. 

There is a rapidly cumulative element somewhere. The whole 
movement is too rapid for selection, especially with the exceed- 
ingly moderate destruction of individuals that sometimes takes 
place. Plants do not acclimate by reason of most of them being 
killed off, yet there is a strongly progressive element involved. 
The inevitable conclusion is, in the opinion of the writer, that 
the chief effects of acclimatization are transmitted. 

Whether this transmission be direct or indirect ; whether it 
be due to the peculiar development of the individual impressing 
itself upon the germ, or to climatic influences, like tempera- 
ture, food, etc., which being allpcrvading, affect the general 
state of life and influence the germ direct, is another and more 
important matter. 

That the simple removal of a part does not affect transmis- 
sion is significant. The old contention that the protoplasm of 



386 TRANSMISSION 

the germ and the protoplasm of the developed body are essentially 
different has long since been disproved. Both are susceptible 
to any influence that can reach them, and in climatic conditions 
generally we have abundant influences of this kind. 

May we not consider as established the possibility that the 
germ itself, and therefore descent, may be directly modified by 
external influences ? How far this may go, and what influences 
are included, is another subject, and one calling for the most 
careful study and requiring the most reliable data as a basis for 
an intelligent opinion. 

The present state of knowledge is insufficient to entirely 
solve the problem, but there is additional evidence worth 
consideration. 

SECTION VI — EVIDENCE FROM HABIT AND INSTINCT. 
IS INSTINCT INHERITED HABIT? 

Habit and instinct both refer to the use which individuals 
make of those racial characters that are capable of action. It 
is a matter of common knowledge that an oft-repeated act 
speedily becomes a habit with the individual, and, as such, 
repeats itself almost mechanically ; so that what was at first 
a nice adaptation of means to end shortly becomes little more 
than reflex action. 

Building upon this fact, it is a plausible assumption that 
what is habit with one generation becomes instinct in the next. 
It is a sweeping but easy generalization that " no distinct line 
can be drawn between instinct and reason" ;i that instinct is 
inherited habit, and reason inherited instinct modified by indi- 
vidual experience. 

This is the position taken by many of the older naturalists, 
especially Romanes, who defined instinct as " reflex action into 
which there is imported the element of consciousness," ^ and 
reason as " the faculty which is concerned with the intentional 
adaptation of means to end." ^ 

^ Romanes, Animal Intelligence, p. 15. 

2 Ibid. p. 17. This volume is perhaps the most extreme exponent of the idea 
of inherited habit, and of intelligence as lying at the basis of all animal activity. 



TRANSMISSION OF MODIFICATIONS 387 

Thus the whole question is up again in this connection. Will 
the habit of the individual be transmitted to its offspring ? Is 
the habit of one generation the instinct of the next ? If so, then 
we have a case of transmission of modifications (inheritance of 
acquired characters) of the most direct and certain kind. 

The answer to the question is important for its own sake, but 
more especially for the light it may throw upon the main ques- 
tion now in hand. To arrive at a safe answer it is necessary to 
give more than a passing notice to the natnir of instinctive acts, 
and to critically determine whether instinct is built upon habit 
or habit upon instinct. 

Nature of instinctive acts. Most acts of intelligent beings 
are performed for a particular purpose and for definite ends. 
Most such acts are controlled by a greater or less degree of 
purposeful adaptation of means to end that involves knowledge 
of results, based on experience and merging naturally into habit. 
Habit is then the aistomajy nse to which the individual puts the 
parts with which it is endowed by nature, after they have reached 
full development. Its chief interest to us at this point arises 
from the fact that another individual might put the same parts 
to a different use, while in instinctive acts use is a function of 
siructtire, and but one set of actions is possible except under 
greatly changed conditions. 

The term " instinctive " is applied to those acts which are per- 
formed without previous experience and perhaps under circum- 
stances that preclude all knowledge of what the result will be ; 
so that, as far as the individual is concerned, there is, and can be, 
no consciousness of purposeful action or of adaptation of means 
to end, and yet the action, often compHcated in the extreme, 
may be eminently adaptive and exhibit every appearance of being 
the act of a most intelligent being. Young mammals suck with 
the lips ; young waterfowls swim and dive, but land birds do not ; 
young squirrels hide objects, and even in a room go through the 
motions of digging and burying ; young chicks have their own 
peculiar cry, and peck at shining objects ; birds build their nests 
without instruction or assistance from older or more experienced 
individuals. These are instinctive acts of the simplest order ; 
many others, however, are extremely complicated. For example. 



388 TRANSMISSION 

an insect burrows a cavity and lays its egg. It then attacks 
another insect, stings it so as to paralyze but not to kill it, drags 
it to the burrow, tucks it in next to the egg where it will serve 
as food to the larva, seals all up, and goes away. 

The yucca moth emerges from the cocoon just as the yucca 
opens its flowers, each for a single night. The female collects 
pollen from one flower and kneads it into a bundle. She then 
flies to another, makes a puncture, and lays her egg among the 
ovules, after which she darts to the stigma and " stuffs the 
pollen pellet into the funnel-shaped opening." ^ It is supposed 
that this is the only way in which the insect reproduces, and the 
chief way in which the yucca is fertilized. 

Here definite and important ends are dependent not only 
upon complicated acts but also upon the serial order of tJieir per- 
fonnanee, — all without previous knowledge or experience on the 
part of the agent, for the female in most cases is performing 
this act for the first time, and in many cases will not live till the 
eggs hatch. Given any amount of intelligence, therefore, she 
could not know the final result of her own industry, although 
the entire process has every appearance of intelligent, even delib- 
erate, action. It is noticeable at once that instincts of this sort 
are concerned with those acts which, like reproduction, are funda- 
mental to race preservation. 

Is instinct founded on habit ? The outcome of most instinc- 
tive acts is so clearly the preservation of life and the good of 
the species, the acts themselves are often so extremely compli- 
cated, their separate steps are so nicely adjusted to the final 
end, their proper serial order is so accurately observed, the 
appearance of deliberate, purposeful action is so genuine, the 
need of intelligent direction at some period of the organization of 
the series is so apparent, the importance of the ends achieved is 
so obvious, and the similarity between the instinct of a race and 
the habit of an individual is so close that many naturalists have 
leaped to the conclusion that instinct is inherited Jiabit ; in other 
words, that what has been found beneficial in the experience of 
individuals has become habitual with them, and through theii: 
descendants it has become the habit of the race. This position 

^ A free transcript from Morgan, Habit and Instinct, p. 14. 



TRANSMISSION OF MODIFICATIONS 389 

was quite generally taken by the older naturalists. As Romanes 
puts it,^ " Instinctive actions are actions which, owing to their 
frequent repetition, become so habitual in the course of genera- 
tions that all the individuals of the same species automatically 
perform the same actions under the stimulus applied by the 
same appropriate circumstances." He adds : " Rational actions, 
on the other hand, are actions which are required to meet cir- 
cumstances of comparatively rare occurrence in the life history 
of the species, and which, therefore, can be performed only by 
an intentional effort of adaptation." 

If, now, instinct be inherited habit, and reason only modified 
instinct, then we have an unbroken chain, from the simplest 
adaptive act up to the highest mental generalization, — all the 
product of inherited experience. This is inheritance of indi- 
vidual modifications (acquired characters) of the most pronounced 
type, and if true, it affords the most important evidence upon the 
question now under consideration. 

A critical analysis of the matter makes clear the fact that this 
conclusion involves the following extreme assumptions, whose 
correctness must be carefully considered and not accepted with- 
out question, as is too often done : ^ 

1. That instinctive acts are performed perfectly at the first 
attempt, — the traditional " unerring instinct." 

2. That they are carried out substantially in the same way by 
all individuals of the race and by the same individual in succes- 
sive performances.'^ 

3. That instinctive acts are always adaptive, thus showing 
their ultimate origin in purposeful acts.* 

4. That habit precedes instinct, and that instinct finds its 
directive force in inherited experience.^ 

It is well to consider these points somewhat carefully. 

Instinct not unerring. The earliest instinct of the young 
mammal is to suck. Moreover, it is an instinct connected with 
the preservation of life ; yet the calf will be entirely satisfied 

1 Romanes, Animal Intelligence, pp. 16-17. 

'^ Read, in this general connection, Habit and Instinct, by Lloyd Morgan, 
especially pp. 29-127. 

3 Romanes, Animal Intelligence, p. 17. * Ibid. p. 15. ^ Ibid. pp. 16-17. 



390 



TRANSMISSION 



with its neighbor's ear, the baby with its own fist, or the young 
lamb with a lock of wool, which, if the mother be young and 
inexperienced, it may suck until it starves. Young chicks will 
pick up and swallow at first whatever attracts their attention, 
— bits of colored yarn, or "nasty" caterpillars, as readily as 
"good " worms ; but they rapidly learn by experience.^ 

The instinct of the young chick is to strike at any small 
object that attracts its attention either by its color or its move- 
ments ; yet the first attempts are extremely awkward and sel- 
dom result in a catch, the bill going some distance to one side 
of the object. Gradually, however, it learns by experience to 
strike accurately.^ 

Walking, flying, swimming, and talking are instinctive acts 
with species possessing the requisite mechanism ; yet the first 
attempts are exceedingly crude, and much experience and prac- 
tice are required before effective proficiency is developed. 

A fair study of the subject can but convince the student that 
instinct is at first but little more than an impulse to action in 
general, which, however, rapidly shapes up into well-ordered 
performance under the corrective influence of experience. 

Instinctive acts are not performed in the same way either by 
all individuals or by the same individual at successive perform- 
ances. To watch the complicated acts of the egg-laying instinct 
in many insects is at first to become convinced that this marvel- 
ous sequence of events is assured only by the highest intelli- 
gence or by an instinct that is unerring in its directive power ; 
yet a little further study will convince the student that these 
complicated instinctive acts are not always carried forward on 
the typical plan, nor are they always successfully executed. On 
the contrary, important, even significant, steps are often omitted 
from the series, and different individuals differ greatly in the 
degree of thoroughness and the rapidity with which the work is 
carried forward. 

For example, Crandall endeavored to note accurately all the 
steps in the process of making the puncture and laying the Q.^g 
of the plum curculio working upon the apple. ^ 

1 Morgan, Habit and Instinct, pp. 40-44, 50. 2 Ibid. pp. 37, 47. 

^ Bulletin A'o. <pS, Illinois Experiment Station, pp. 500-504. 



TRANSMISSION OF MODIFICATIONS 391 

Of many attempts to watch and record the process from 
first to last, only three were successful in covering the entire 
period. The rest were fragmentary, covering only portions of 
the process. This was owing to the difficulty of keeping the 
insect under focus for the fifteen to twenty-five minutes re- 
quired for the complete operation without disturbing its work. 
The record of the observer is as follows : 

In the first observation the female moved about the apple for several 
seconds, keeping the end of her beak in contact v^^ith the surface, as if 
seeking a favorable spot. When the exact spot was decided upon, the 
minute jaws at the end of the snout began a rapid movement which quickly 
made an opening through the skin. This opening was no larger than neces- 
sary for admission of the tip of the beak. No skin was removed ; it was 
simply torn and thrust aside to give access to the pulp below. Later, as 
the excavation proceeded, the broken skin was seen as a sort of fringe 
around the beak at the surface of the fruit. As soon as excavation in the 
pulp was commenced, the beak was deflected backward so that the work 
was carried on under the insect, just beneath the skin and nearly parallel 
with the surface. As the work advanced, the opening through the skin 
became slightly enlarged by lateral motions of the beak. The pulp was 
all eaten as excavated. During the process the beak was not once with- 
drawn, nor was there any cessation of motion. When the excavation of 
the cavity was completed the beak was withdrawn by a quick motion, the 
insect turned about, adjusted the tip of the abdomen to the opening and 
deposited an egg, which was forced to the extremity of the excavation by 
the ovipositor. The insect now rested without motion for two minutes; 
then, turning again, proceeded to cut the crescent in front of the ^gg. 
This crescent puncture was not wholly a separate puncture, but, starting in 
the original opening through the skin, was cut laterally in either direction, 
partly by the jaws and partly by crowding the beak first one way and then 
the other. The direction of the beak was but little deflected from the per- 
pendicular, and the cut was made as deep as the length of the beak would 
allow. The pulp torn away in making the crescent was eaten, just as was 
done in excavating the egg cavity. The crescent completed, the insect 
walked away, drew the legs closely under the body, and settled down, 
apparently to sleep. The time occupied in the process described was dis- 
tributed as follows : 

Excavating egg cavity 9 minutes 

Deposition of egg i minute 

Rest 2 minutes 

Cutting the crescent 3^^ minutes 

Total 15^ minutes 



392 



TRANSMISSION 



The egg cavity was cylindrical, with a rounded bottom, and by measure- 
ment was found to be 0.04 inch in depth. The tgg when deposited very 
nearly filled the cavity. 

The second observation of the complete process was nearly identical 
with the one described. The insect spent no time in choosing the exact 
spot, but went to work at once. It worked in a more leisurely way and did 
not excavate as deep an egg cavity. Eleven minutes were spent on the 
cavity, two minutes in depositing the egg, two in rest, and four in cutting 
the crescent, — a total of nineteen minutes. The egg cavity measured 0.035 
inch in depth and was completely filled by the egg. On completion of the 
process the insect moved a short distance and immediately began a second 
cavity. 

Essential differences from procedure in the two preceding cases were 
noted in the third complete observation. Excavation of the egg cavity was 
the same, except that it was deeper in the pulp and of greater extent. After 
depositing the egg the beetle turned, and with her deaA worked the egg 
back to the bottom of the cavity. T/ieu she began tearing off bits of skin 
and pulp, which were carefully packed in., above the egg, until the cavity was 
full} Following this, the crescent was cut in much the same manner as in 
the preceding cases. Then she appeared to make a final inspection, and 
added some further packing above the egg. Finally the work appeared to 
be satisfactory and she walked away and began a second puncture. The 
time consumed in this process was longer than in the others, and was divided 
as follows : 

Excavating egg cavity 12 minutes 

Depositing egg i .' minutes 

Placing the egg with the beak .... 2 minutes 

Packing the cavity 4 minutes 

Cutting the crescent 4 minutes 

Finishing touches 3 minutes 

Total 26i minutes 

Among the many cases where only part of the process was observed 
some anomalies were noted. In two cases the insect walked away im- 
mediately after depositing the egg and made no crescent cut. In three 
cases beetles were seen to cut crescents and, moving a short distance, 
begin other punctures. These crescents had no egg cavities and no eggs 
were deposited in them. In two cases eggs were found deposited directly 
in crescent cuts, neither of which had the usual egg cavity. Marked varia- 
tion in depth of the egg cavity was frequently observed. Not infrequendy 
the cavity is so shallow that the tip of the egg protrudes, and sometimes 
its depth is nearly equal to twice the length of the egg. Packing the egg 
cavity with pieces of pulp is a coni?non, but not universal, practice; often 
this is neglected, even where the cavity is deep. . . . 

1 Italics are mine. 



TRANSMISSION OF MODIFICATIONS 393 

When reading of the various processes and acts in insect economy, as 
observed and recorded in published life histories, it is quite natural to 
suppose that these processes are fixed, absolute, and unchangeable, while 
as matter of fact many of them are subject to modifications. Sometimes 
these variations have apparent reason in surrounding conditions, and again 
they can be ascribed only to individual peculiarity. . . . 

A crescent puncture is usually supposed to represent an egg or an 
attempt at egg laying, but this does not always hold true, because, as 
stated above, some crescent cuts are made without the accompaniment of 
egg laying. On May 27, 1903, fallen apples, twenty-five in number, were 
picked up at random for examination of the crescent punctures. Nearly 
all were more or less punctured by the apple curculio, but these punctures 
are not considered here. Two fruits bore apple-curculio punctures only, so 
that the number examined for crescent marks was twenty-three. On the.se 
twenty-three apples were fifty-eight crescent marks, or 2.52 to each apple. 
There were also thirty-five feeding punctures made by the plum curculio. 
Of the fifty-eight crescent cuts, fourteen, or 24.14 per cent, had no egg 
cavities and contained no eggs. The remaining forty-four crescent cuts 
had forty-five egg cavities. Some variation in the location of the egg 
cavities was observed ; usually they occupied the center of the crescent, 
but some of these were not so situated. Of the forty-five egg cavities, 
thirty-four, or 75.56 per cent, were located at or near the center of the 
crescent ; eleven, or 24.44 per cent, were located near the ends of the 
crescents. In one case there were two egg cavities within one crescent, 
one on each side halfway between the center and tip. By another modifi- 
cation one of the egg cavities, instead of being excavated from the surface, 
was excavated from the bottom at the center of a crescent cut. It was of 
usual dimensions, extended back obliquely towards the surface, and con- 
tained an egg. Evidently in this case the crescent was cut first and the 
cavity excavated afterwards. . . . 

The statements we have quoted regarding the details of oviposition of 
the plum curculio, together with the observations recorded, indicate varia- 
tion in details sufficient to confuse the layman and even to puzzle the 
expert if he seek to cover rightly any detail with a general statement that 
will fit all cases. Two conclusions are open : either some individual insects 
have faulty instincts or there is more than one acceptable way of performing 
several of the details of oviposition. The writer accepts the latter conclusion. 

From this it is seen that the somewhat compHcated process 
of Qgg laying varies greatly in detail ; that the time consumed 
varies at least from fifteen and a half to twenty-six and a half 
minutes ; that important details are often omitted ; and that in 
a large proportion of cases even the final object is not attained. 
Knowing these variations, one is not surprised to learn that of 



394 TRANSMISSION 

the twenty previously recorded observations no two agreed, and 
not one gave a complete account of what may be called the 
typically instinctive process. Bearing all these facts in mind, we 
are not to suppose that still more complicated processes are 
successfully carried forward in every instance, as we have been 
led to infer. Instinct is, therefore, not unerring, nor does it 
insure uniformity of procedure. It looks as if important links 
in the chain of impulse may be omitted, or, if the series is inter- 
rupted for any cause, it may be resumed at almost any point. 
Certain it is that different series are far from uniform and that 
very many of them fail of their evident and final object. 

Instinctive acts are not always adaptive ; their origin is there- 
fore not in purposeful acts. It is of necessity true that in most 
cases instinctive acts are for the good of the species and, there- 
fore, by definition, adaptive. If they were not for the good of 
the species they would speedily lead to extinction, which is but 
another way of saying that instincts not adaptive have long 
since been blotted out by selection, along with the individuals 
in which they arose. 

That such non-adaptive instincts exist, however, is easily 
shown. For example, when the moth flies into the flame and is 
killed, by no stretch of the imagination can this be called an 
adaptive act ; nor can it be conceived as having arisen in the 
purposeful acts of its ancestors. It never could have served 
any but an evil purpose to the race, and the only element that 
now stands in the way of the utter extinction of races possessing 
this instinct is the relative infrequency of the naked flame, so 
that comparatively few individuals suffer, — too few to affect 
either the race or its instincts. We must, therefore, look farther 
than habit for the origin of instincts. 

Instincts originate in reflex action not in habit. If a piece of 
meat be laid upon the tentacles of an actinian they will imme- 
diately contract, infolding the meat and carrying it into the 
mouth. If a piece of paper be laid upon the tentacles no action 
follows ; but if the paper be covered with the juice of meat the 
action is the same as if the piece were valuable for food. 
Tentacles that have arisen from a wound in the side of the body 
will react to meat and meat juice as do the normal parts, 



TRANSMISSION OF MODIFICATIONS 



395 



infolding and pressing the piece against the body as if endeavor- 
ing to tuck it into a mouth, though none is present.^ Here it is 
not intelligence that affords the basis of muscular contraction 
but cJicinical action of the meat juices upon the muscle fibers of 
the tentacles. The same principle governs motion and secretion 
in insectivorous plants, to which no one would ascribe even the 
elements of intelligence. Odors excite the salivary glands and 
make the mouth water, but it is contact that starts the secre- 
tion of gastric juice in the stomach. 

Light stimulates specific reactions in many forms of proto- 
plasm, and many tissues contract under its influence. It is this 
contraction that causes the bending of stems toward the light. 
The iris of the eye contracts, not by nervous impulse but by 
the action of the light, causing, directly, muscular contraction. 
Loeb reports ^ that he has often observed the contraction of the 
iris of dead sharks under the influence of light " several hours 
after death, when signs of decompositioji had already begun 
to appear." 

Long-bodied insects, if lying with the side to the light, will, 
because of this, have their bodies bent, with the concave side 
next to the source of light if positively heliotropic. Whenever 
they move in this condition they must of necessity move in a 
curved instead of a straight line, until such time as they are 
headed directly toward the light. From that time the body is 
equally illuminated on both sides. It therefore becomes and 
remains straight, so that future motion must be in a straight 
line, any deviation being quickly corrected by the unequal illumi- 
nation of the body. It is this series of facts, arising from the 
natural relation between light and protoplasm, and not curiosity, 
that accounts for the flying of the moth into the candle. Nega- 
tively heliotropic animals would of course behave in exactly the 
opposite manner, but for the same general reasons. 

Insects and small worms are said to burrow into dark places 
for the purpose of hiding. This cannot be true, for under direct 
experiment small animals often emerge from darkness to light, 
from hiding to exposure, under the impelling force of an in- 
stinct to bring their bodies into contact with as many surfaces as 
1 Loeb, Physiology of the Brain, pp. 4S-54. ^ Ibid. p. 40, 



396 



TRANSMISSION 



possible. In a box they will crawl along the bottom till they 
come to a side. Here they can touch two surfaces, and motion 
will then be along the groove where the side meets the bottom 
until they reach the corner, where a third surface joins, when 
they are likely not to turn the corner (unless impelled bysome 
stronger instinct) but to come to rest in contact with three 
surfaces, this affording, apparently, the highest attainable satis- 
faction. If a tubular opening be found, insects of this instinct 
will crowd into it, if possible, or at least make the attempt.^ 
This instinct to seek greater comfort by getting snugly placed 
in contact with foreign bodies is present in the higher animals 
and in man, and it accounts for many of the movements and 
resting positions so commonly seen. 

That this action is not the result of a purpose to hide is 
evidenced by the fact that neither light nor darkness has any 
effect upon it, and that the instinct is not changed even by the 
removal of the brain. In nature, of course, places that will satisfy 
this instinct are generally shut away from light, and insects so 
bestowed are also hidden, — a fact that has given rise to the 
tradition that the purpose was to secrete themselves from pred- 
atory enemies. Of course the tradition itself is not consistent, 
for intelligent animals seeking food soon learn the favorite haunts 
of their prey. They therefore know precisely where to look for 
them and speedily turn them out. 

We have already seen that protoplasm may be excited to 
action by a great variety of external agents (light, heat, elec- 
tricity, chemical substances) ; that the character of protoplasmic 
activity may be modified by certain of these external forces, 
notably light and chemical attraction ; that the direction of 
movement or of growth may also be influenced by the same 
class of agents (light, chemical substances, heat, gravity) ; and 
that in all these ways the activities of living beings are largely 
dependent upon the nature of the outside forces with which they 
come into contact. Here lies, to a very large extent, the initial 
cause of those external acts we ordinarily speak of as instincts, 
and the remaining elements of causation are to be sought in the 
internal mechanism of the creature. In all likelihood it is not 

1 Loeb, Physiology of the Brain, p. 93. 



TRANSMISSION OF MODIFICATIONS 397 

too much to say that in the last analysis i7istinct is a function 
of stnictinr ; that the ultimate causes of instinctive acts lie in 
the nature atid the surroundings of the protoplasm, — its internal 
activities upon the one hand and its natural reactiojis to accidental 
contact with outside forces upo7i the other. 

If this be true, then the causes of instincts lie in the structure 
of the organism, — using the word "structure" in its broadest 
sense, chemical and physiological as well as anatomical. Thus if 
a new creature should suddenly be created, its instincts could be 
fairly well foretold by any one who knew the morphology of its 
structure and the nature of its protoplasm. Three fundamental 
facts should be borne in mind in this connection : 

1. Any living being will make use of any organ, part, or 
faculty with which it is endowed by birth. 

2. The impulse to make use of a part may arise either from 
within (desire) or from without (light, heat, chemical action, 
gravity, electricity, contact). 

3. Manifestly the acts of an organism are limited to its natural 
organs and faculties. Therefore instincts, hke intelligent acts, 
differ, being restricted to the range of natural endowment, — a 
restriction which no amount of " willing " will remove or modify. 

Intelligence not necessary to the control of even complicated 
acts. At first thought it seems incredible that a long and com- 
plicated series of acts, culminating in a purposeful end, can be 
directed by any other agency than intelligence. Yet such is the 
fact, and a mistake at this point has led more than one evolu- 
tionist into fatal error. 

When we see an insect light upon a particular part of a partic- 
ular animal, sting it perhaps in such a manner as to paralyze but 
not to kill, drag it to a cavity wherein eggs have been deposited, 
store it away as food for the larvae, seal all up safely as if with the 
greatest care, it is difficult not to attribute the highest intelligence 
and the most careful foresight to so remarkable a series of acts. 

Yet we are not to be deceived by the attitude of busy pre- 
occupation or the appearance of intelligent effort. Acts as com- 
plicated as these are going on about us every day, with no sug- 
gestion of intelligent control. The growth of the embryo in 
utero, and the vital processes generally, are even more orderly 



398 TRANSMISSION' 

and complicated than those semi-mechanical acts connected with 
the deposition of eggs and the care of young, which are them- 
selves in their essence not far removed from vital processes. 

All motion is reducible to irritability and contractility of 
protoplasm as its ultimate cause, and any impulse that will pro- 
duce this effect will lead to action. Furthermore, this action 
must, from the nature of the case, be characteristic of the 
organism and its peculiar mechanism. 

It has been held that all muscular activity must have its origin 
in a nerve stimulus of some sort. That this is erroneous is self- 
evident. Muscle tissue, unsupplied with nerve, is still contract- 
ile, and the impulse can still be supplied from a variety of 
sources (heat, light, electricity, contact). 

Nervous impulse is but one out of many stimuli to muscular 
contraction, or other activity of living protoplasm, though it is 
the most rapid and direct, and the one most readily under con- 
trol of the mind and the will. Restating the proposition, nervous 
mechanism is not necessary to motion, not even to coordinated 
motion of a high degree, but it is necessary to the highest coor- 
dination of the most complicated organisms ; it is necessary as 
the means by which the will may quickly reach all parts of the 
machine and direct or set aside mere instinctive motion ; it is 
necessary for the realization of all the possibilities of which a 
highly organized structure is capable ; it is not necessary to 
action, or even to a high degree of complication in action. 

Any effective impulse will serve to stimulate to activity ; 
and, in general with all complicated actions, each act becomes 
the impulse for the next. If the heart of a frog be cut into sev- 
eral pieces these will all beat rhythmically, " but the number of 
contractions will vary in the different pieces. The sinus venosus 
beats most rapidly, and the number of its contractions in a unit 
of time equals that of the heart before it was divided. TJius ive 
see that the zvhole heart beats in the rhythm of the part that has 
the ■}naximum number of contractions per minute. From this we 
must assume that the coordination of the heart's activity is due to 
the fact that the part whicJi contracts -most frequently forces the 
other parts to contract in the same rhythm y ^ 

1 Loeb, Physiology of the Brain, p. 25. 



TRANSMISSION OF MODIFICATIONS 399 

This shows, not only that a center of coordination exists in 
the organ itself, independent of nerve centers, but that the 
action of one part becomes the impulse for exciting action in its 
neighboring part. 

Hydromedusae of different rates of pulsation were united in 
pairs in Loeb's laboratory by the process of grafting. When the 
union was complete along nearly all the cut edge the whole 
beat synchronously, but when the union covered but a small 
area the two beat separately with a different rhythm.^ 

The heart of the ascidian is an elongated tube, beating so as 
to send the blood alternately from left to right and from right 
to left ; that is, the impulse seems to originate at one end for a 
time, and then, after several hundred beats, to shift to the other 
end. It was found that the " area of impulse " was confined to a 
short section at either end ; that each of these sections, if cut 
away, continued to beat rhythmically, but that the longer middle 
part seemed incapable of contraction without external stimulus. 
Commenting on the fact, Loeb says : ^ 

These experiments, it seems to me, leave no room for doubt that the 
change in the direction in the contraction of the ascidian's heart is deter- 
mined by each of the two ends getting the upper hand alternately and forcing 
the other center to act in its rhythm for a time. This " getting the upper 
hand " might possibly mean nothing more than that one end gains the time 
in which to send off a wave of contraction before the other end begins to 
contract. For this it is only necessary that a single heart beat of the lead- 
ing end be delayed or fail entirely, a phenomenon that also appears occasion- 
ally in the human heart. 

Locomotion in the earthworm is by a series of elongations and 
contractions of the successive segments of the body, in regular 
order from the front backward. Nobody ever supposed this serial 
order to be controlled by conscious intelligence, but it has been 
assumed to be due to the control of nerve fibers from the ganglia 
along the dorsal surface of the body. If, however, the worm be 
cut in two and the parts united by threads, locomotion is entirely 
successful, even though a considerable space intervenes between 
the pieces. In this case contraction proceeds backward, seg- 
ment by segment, as in uninjured worms, suffering no special 

1 Loeb, Physiology of the Brain, pp. 26-27. ^ ibid. pp. 27-29. 



400 TRANSMISSION 

interruption at the point where the nerve connection is severed. 
The thread serves perfectly to carry the impulse over from the 
last segment of the anterior piece to the first of the posterior. 
The unavoidable conclusion is that at least from this point back- 
ward each segment derives its impulse not from ncri'e fibcjs but 
from the segment just ahead ; in other words, that the motion of 
one part becomes a stimulus to appropriate action in a neighbor- 
ing part. 

It is reported that Ribbert transplanted a milk gland to the 
ear of a guinea pig, and that when the individual became preg- 
nant the gland commenced to secrete milk. Whatever the 
nature of the stimulus, it was clearly independent of nerve 
impulse.^ 

It is a well-known fact that if an ant be removed from its 
nest for a time and then put back, it will be critically examined, 
but will be received again ; if, however, a stranger ant be intro- 
duced, it will at once be attacked and killed. How is the differ- 
ence detected } This question is largely answered by the fact 
that, if the ant belonging to the nest be smeared with the juices 
of a crushed stranger, it will at once be attacked and killed as 
would the real stranger.^ Clearly it is by the odor that the ants 
detect the difference, much as the dog recognizes his master in 
daylight or in the darkness, or follows a trail along a crowded 
street. All this shows that even a slight cause, like odor, may 
serve to start the operation of a train of most remarkable re- 
flexes, which, once started, proceeds automatically, each act 
operating as a stimulus to the next. 

This fact is further illustrated in the case of dogs deprived of 
large portions of the nervous system. Individuals that have 
lost the spinal cord " almost up to the medulla " may live for 
years and perform all normal functions.^ 

Goltz entirely removed both hemispheres of the brain from a 
full-grown dog. The first effects of so violent an experiment are 
apparently disastrous, but if skillfully done the shock soon sub- 
sides and all normal f mictions of the body proceed as bifore. 
That is, the animal performs the external acts of eating, urina- 
tion, defecation, etc., the same as when in possession of the brain, 

^ Loeb, Physiology of the Brain, p. 206. ^ ibid. pp. 220-221. ^ ibid. p. 43. 



TRANSMISSION OF MODIFICATIONS 40 1 

and apparently according to the same train of reflexes that provide 
in hfe generally for such important vital processes as the pulsa- 
tion of the heart, characteristic action of the various glands of 
the body, the movements of the intestines, etc. All traces of 
memory were gone, and the dog could not recognize its master. 
It would avoid objects in walking, but could not recognize food. 
If, however, the food were brought in contact ivith the nose or 
placed in the mouth, the jaws commenced to work and the food 
was swallowed and digested as by any other dog.^ 

Dogs in this condition live for months or for years, and perform 
all the functions of normal animals not requiring intelligent 
action. All this shows to what extent vital actions are a series 
of reflexes constituting a train, in which, if one member be started 
by appropriate stimulus, all the rest follow automatically. 

Instinct not founded on habit. The facts that have been cited 
certainly show that instinctive acts are nothing but the putting to 
use of parts in possession of the individual and capable of action. 
They are in that way spontaneous, and whatever meaning or 
special significance may seem to be involved, it is to be sought, 
not in the impulse to tJie act, but farthc}' back in the circnmstances 
and causes that led to the development of the parts, each with its 
charactenstic capacity. A multitude of causes have taken part in 
the selective processes by which the several organs and parts of 
a body have been developed, each capable of performing a special 
act, either independently or as a part of a complicated series ; 
but, once assembled, nothing is more natural than that each 
should perform its proper service, and any stimulus sufficient to 
start the machinery will of necessity insure the whole train of 
appropriate results. 

Nor are we to be deceived by the appearance of intelligence 
as the acts proceed. The busy preoccupation of the insect 
engaged in one of the more complicated processes of egg laying 
has all the semblance of the highest intelligence, but we must 
not forget that in many cases the individual must be entirely 
ignorant of the final result ; it will be dead before the eggs 
hatch ; it lives but a single season and, therefore, neither it nor 
its ancestors ever saw a larva ; it is simply playing its role in a 

1 Loeb, Physiology of the Brain, pp. 246-24S. 



402 TRANSMISSIOiN 

wonderful series of which it is itself but a part, and of whose 
beginning and end it is alike ignorant. 

The instinct to suck cannot be conceived as founded on habit, 
because sucking is not a life habit with any individual. It is 
practiced but a brief season after birth, and then abandoned, 
leaving no trace or even impulse behind. 

It is difficult for us to dissociate these complicated acts from 
the idea of intelligent control. Yet many of them are performed 
by plants, in which there is not so much as the beginnings of a 
nervous system, the impulse traveling from cell to cell, as it is 
entirely capable of doing in animal tissue, but at a rate easily 
overtaken by nerve transmission, whenever the latter is superim- 
posed by the will or otherwise. 

Again, we must consider the exceedingly complicated nature 
and serial order of the vital processes generally. Most of these 
processes, it is true, aside from copulation, the laying of the egg, 
and the care of the young, are carried on inside tJic body, and 
therefore out of sight of the observer. If we could by some 
mental microscope see not only the pulsation of the heart, the 
movements of the stomach and intestines, and the discharge of 
accumulated secretions, but also the internal acts of secretion 
going on within the various glands of the body, with the associated 
protoplasmic motion and cell division, actively accompanied by 
the careful division of the chromosomes into exactly equal por- 
tions qualitatively as well as quantitatively — if we could see 
all this as we see external instinctive acts, we should be led to 
marvel at the mystery and the complication of vital activity in 
general. We should involuntarily seek a basis of intelligent con- 
trol zvithiji the organism, whereas we kjiotv that the proper 
place to seek causation is outside the creature in the forces 
that shaped its development and in the higher power that en- 
dowed it all with life, whose characteristic act is motion and 
appropriation of new material. We are, therefore, not to be 
misled by the complexity of acts having the appearance of 
intelligence. 

We have been led to project intelligence too far down the 
scale. It may, if present, take hold of and overrule most (not all) 
instinctive acts, but the vast majority of organic activities go on 



TRANSMISSION OF MODIFICATIONS 403 

without it.i Young things have httle or no sense of fear at 
birth, and at the first consciousness of fear make nothing Hke 
intelligent discrimination. The young chick, so Lloyd Morgan 
tells us, is as much afraid of a flying newspaper as of a hawk, 
and has no preconceived notion of the danger from bees, which 
can sting, as compared with that from flies, which are harmless. 
Its first fears are of "largish things," but experience rapidly 
informs it of specific things. It has at first no appreciation of 
water as water, but when it accidentally pecks at a shining drop 
and wets the bill, the presence of the water starts the series of 
reflexes and the chick holds up its head to swallow, or, if a duck, 
it "shovels," — each organism reacts in its own characteristic 
manner, — and both learn rapidly by experience.^ 

Habits follow and are founded upon instincts. The true order 
seems to be that the earliest attempts are instinctive, but that 
they are rapidly shaped up and perfected by experience, and in 
this condition they become habitual. It also appears that no 
exact line can be drawn between what we call instinct and what 
is nothing but response to stimuli. Manifestly we have applied 
the word "instinct " to those reflex acts that have the appearance 
of being purposeful. It would apply equally as well to many acts 
clearly reflex, and when it is shown that these so-called instinc- 
tive acts are themselves only reflexes and can be performed per- 
fectly in the absence of all possible application of intelligence, 
either on the part of the individual or of its ancestors, it appears 
that our present use of the word is a convenience rather than a 
fair mark of a scientific distinction. 

The theory, therefore, which places habit at the point of origin 
of instinctive acts clearly takes it out of its proper order in the 
series. It is a property of the individual rather than of the race, 
— except as we speak of the habit of a race, meaning there- 
by the habit developed by all or most of the members of the 
race. The common development of such a habit is not unnatural 
since all of the individuals of the race possess the same organs 

^ The action of the heart and of the secreting organs is beyond the control of 
the will, and that of the intestines is largely so ; but many parts of the organism 
are under control either of the will, of impulses internal to the part, or of causes 
external to the organism. 2 Morgan, Habit and Instinct, pp. 40-90. 



404 TRANSMISSION 

and are for the most part subjected to the same surrounding 
conditions. 

Carefully examined, this field, interesting as it is of itself, is 
barren of evidence upon the transmission of habits, though it 
is the one most often appealed to for proof of the inheritance 
of acquired characters. The error lies in assuming a causative 
relation between two acts which are similar. It is true that the 
habits of the individual and the instincts of the race are similar. 
They could not be otherwise, seeing that both depend upon the 
presence of suitable organs, without which the particular act 
would not be possible, and with which it is certain to appear 
whenever suitable stimulus is encountered ; but habit is founded 
upon instinct and not instinct upon habit. 

The conclusion which seems inevitable is this : tJiat breeders 
need have no fear that the Jiabit of an individual, as suchy zvill be 
inherited by its offspring ; but the fact that the Jiabit developed at 
all is sufficient reason for knoiving that its develop^nent is always 
possible in the family line, ivhcnever suitable conditions arise. 

The attention of the student is called to the fact that while 
we have shown that instinct is not the result of habit, and there- 
fore that its existence is no proof of the transmission of habitual 
acts, yet this does not show whether or not the habitual use or 
non-use of a part will affect the intensity of transmission of that 
part, or the tendency to make use of it. Having put instinct 
behind us where it properly belongs, we have now to inquire into 
the effects of use and disuse. 

SECTION VII — EVIDENCE FROM USE AND DISUSE 

The question is not whether use develops and disuse leads to 
non-development or degeneracy. The facts on that point are 
already well known. The inquiry is whether the effects of use 
and disuse are transmitted ; whether their influence is direct, 
not merely indirect by rendering the individuals less or more 
able to meet the demands of selection ; whether specialization 
of a part is in any way due to use, aside from its effect in 
developing individuals separately and aside from its connection 
with increased rigor of selection ; whether generalization and 



TRANSMISSION OF MODIFICATIONS 405 

degeneracy — beyond under-development in individuals, or as 
associated with cessation of selection — are in any way the result 
of disuse ; whether an individual is a better parent after a long 
course in exercise or training, or a worse one after a long life 
of idleness, than the same individual would have been before ; 
whether a race horse will transmit better speed after he or she 
has been " developed," and has made a record on the track, than 
he or she would have transmitted if never tracked ; whether the 
later children of a studious or of an athletic man (or woman) 
will be born with more ability in these directions than the earlier 
ones, and whether the younger children of criminals are more 
inchned to criminality than are those born before the criminal 
instincts were fully developed in the parents. The real question 
is this : Is transmission augmented or lessened by the degree of 
development to ivhicJi raeial cJiaractcj's have attained in the indi- 
vidual before parentage, and without reference to seleetiou ? 

In the opinion of the writer there is not yet sufficient evi- 
dence on which to base a final decision, and much as we all 
desire a settlement of the matter, and much as we need to 
know what the real truth is, nothing is gained by passing pre- 
mature judgment, and the question must be left for the time 
unanswered. 

For the present the student must content himself with learn- 
ing to know the field of discussion, and, inasmuch as he must 
hold his opinions in abeyance, it is important that he know the 
arguments pro and con. If he do this, and keep his ear to the 
ground, he will find the question clearing up rapidly in the near 
future ; we may be nearer its solution than the most careful 
biologists have yet dared to hope. 

Not going back of the fact that no somatic variation can pos- 
sibly become blastogenic, Weismann and his followers deny /'// 
toto all possibility of such transmission, although Weismann him- 
self has admitted, as a result of his own experiments with the 
colors of butterflies as dependent upon temperature, that such 
all-pervading conditions as heat may penetrate to the germ and 
affect its character as well as that of the tissues of the body. 
In the opinion of many recent writers the list of " all-pervading" 
influences includes much more than temperature alone. 



4o6 TRANSMISSION' 

Weismann's exact words concerning the two varieties of 
butterflies — the darker Italian and the lighter German — are 
as follows : ^ " The two varieties may have originated owing to 
a gradual cumulative influence of the climate, the slight effects 
of one summer or winter having been transmitted and added to 
from generation to generation"; and again,^ "In many other 
animals and plants influences of temperature and environment 
may very possibly produce permanent hereditary variations in a 
similar manner" ; and still again, ^ "Many varieties of plants 
may also be due wholly or in part to the simultaneous variation 
of corresponding determinants in some part of the soma and in 
the germ plasm of the reproductive cells, and these variations 
must be hereditary. Temperature^ and nutrition in its tvidest 
sense, affect the wJiole body of the plant — tJie somatic cells as 
well as the germ cells." ^ 

In all this it must be noted that Weismann limits action of 
this kind to such external influences as are able to penetrate the 
organism and affect the germ plasm directly ; whether an influ- 
ence does this is to be determined in every case by direct ex- 
periment, and is not to be assumed from the effect of the same 
influence upon mere body development. 

These citations from Weismann, while not especially bearing 
upon the topic of use and disuse, are introduced because his 
position as the leader in opposition to the theory of the trans- 
mission of modifications due to external influences is often mis- 
understood. They are introduced at this point because it is 
concerning use and disuse that the most vigorous discussions 
have arisen. 

Those believing in the transmitted effects of use and disuse 
base their belief mainly upon the method of proof by instance, 
and most of them cite instances that were far better omitted. 
As long as one side depends upon simple enumeration, and 
the other mainly upon abstract reasoning, we are not likely to 
get ahead. As all forms of acquired characters are discussed 
together, it is practically impossible to cite references dealing 
exclusively with use and disuse ; but in order that the student 

1 Weismann, Germ Plasm, p. 400-406. ^ Ibid. p. 406. 

2 Ibid. p. 405. * Italics are mine. 



TRANSMISSION OF MODIFICATIONS 407 

may do his own thinking, some of the principal references relat- 
ing in part to use and disuse are given in the footnote.^ 

It is important that we know the truth in this matter if pos- 
sible. If the perfection of development that comes only with 
use is to any extent transmitted, then we must put our speed 
horses through a long course of training and develop them fully 
before we may hope that they will transmit maximum speed. 
If this theory be correct, then the heifers from a mature cow 
that has been long in milk and made record, will be capable 
of developing into better milkers than would be possible if 
the dam had never made extreme records, or than would be 
possible with the earlier calves from the same cow (before the 
extreme records were made). Manifestly the age of the bull 
will not count, as he is incapable of developing this particular 
character. All he can do is to transmit, unaugmented and 
unchanged, the hereditary faculties of milk production exactly as 
they descended to him. In meat production of course, as in speed, 
the case would be different, as both sexes may be conceived as 
capable of adding to (.?) or detracting from (?) the racial intensity 
by reason of their own development or lack of development. 

This subject is now under investigation, and while the point 
would seem to be easy of determination, yet it involves the care- 
ful study of all the progeny of many individuals both before and 
after development. On this point, however, evidence may be 
expected at no very distant date. 

Effect of development upon transmission of speed in horses. 
In a recent series of articles,^ Casper L. Redfield takes the 
position that the effects of speed development are transmitted, 
and he cites numerous instances calculated to show that maxi- 
mum speed is transmitted only from sires with long and 

^ Against transmission : Weismann, Germ Plasm, pp. 392-410. In favor of 
transmission : Romanes, Darwin and After Darwin, II, 60-287 ; Cope, Origin of 
the Fittest, pp. 194-203, 405-421, and Primary Factors of Organic Evolution, 
pp. 246-384; Eimer, Organic Evolution, pp. 153-173, 205-221. Non-Partisan : 
Lloyd Morgan, Habit and Instinct, pp. 280-322 ; Vernon, Variation in Animals 
and Plants, pp. 352-370. 

2 Mr. Redfield's theories are best set forth in a series of articles entitled " Evo- 
lution of the Setter," in Amerha/i Field, LXII, Nos. 25-27, and LXIII, Nos. 1-9. 
They are further set forth in a series entitled, " Breeding the Trotter," published 
in The Horsetnan, XXV, Nos. 19-34. 



4o8 TRANSMISSION 

honorable racing records. The studies would be more conclu- 
sive if they included larger numbers of examples, and if these 
were thrown into two classes, — one gotten after the records 
were made, the other gotten by the same sires before their 
development. 

Mr. Redfield conceives that the sire or dam that is constantly 
worked up to a safe limit develops thereby a larger stock of 
what he calls "dynamic force," and that transmission is in pro- 
portion to the extent of this force present at the time of procre- 
ation. There is no need of involving the subject with new terms. 
What is in Mr. Redfield's mind is doubtless the same thought 
that lies at the basis of Cope's theory of growth force, which is 
one of the strongest of what may be called the dynamic theories 
of evolution. Everybody recognizes a dynamic basis in trans- 
mission, — that which is connected with the intensity of the 
vital processes. Many forces cause that intensity to vary, and 
the important question is whether exercise, use, extreme devel- 
opment in the individual, is one of them. Mr. Redfield's articles 
may be read with profit ; whether or not all his conclusions will 
stand is another matter. The articles are chiefly useful for the 
large mass of facts presented, which, good as they may be, are 
not yet sufficient to maintain his theories or to answer the ques- 
tion that horsemen would like to have settled. 

Certain outside considerations must be borne in mind in 
studying this subject : 

1. The better the sire as to speed, the better will be his 
opportunity to get speed, for the more numerous will be his 
offspring and the better will be the class of mares offered. The 
same principle holds true as to the dam, for only a good one is 
worth the fee for a high-class staUion ; in other words, the sires 
and dams with records have better opportunities to produce 
than do those equally good but without records. Because of 
this fact the get of one animal must be compared, not ivitJi tJiat 
of another, but zvith his own of a later or earlier elate. 

2. Speaking generally, the get of the best horses later in life, 
after they are knozvn to be valuable, will be better trained and 
better developed than the get of the same animals earlier in 
life and in the hands of more ordinary horsemen. 



TRANSMISSION OF MODIFICATIONS 409 

3. So much of this exercise, or development, as contributes 
simply to constitutional vigor and good health will have its effect 
under quite another principle. Moderate exercise over against 
absolute inactivity should show some results, but this is entirely 
outside the present inquiry. What we desire to know is whether 
the extreme developtnent of a faculty in an individual will aug- 
ment its transmission above what would otherwise have been the 
transmitting power of that individual. 

Mr. Redfield's conclusion that this transmission is limited to 
the same sex — that the development of a sire affects only his 
male offspring — does not rest upon good grounds, and is against 
what is generally known as to sex transmission. It will be seen 
later that sires are slightly but not noticeably prepotent over 
dams in male offspring, and vice versa ; but the difference is 
slight, and not marked, so far as it has yet been studied by the 
statistical method, which is the only reliable one for the deter- 
mination of questions of this character. 

Effect of development upon the transmission of milking quality. 
It is a widespread belief that a heifer will make a better cow if 
brought into milk at two years of age than she will make if her 
milking powers are not developed till later. Will her later 
calves, dropped say at six years of age, be influenced by the fact 
that she was a cow at two years of age rather than not until four 
or five } The question cannot be answered at present, though 
records are accumulating which will almost certainly afford an 
answer in the near future. In the meantime it is both fruitless 
and hazardous to speculate. We must turn in another direction 
for the only known evidence that is valuable, and reason by 
inference from the behavior of characters under degeneration. 

SECTION VIII — EVIDENCE FROM DISAPPEARING 
ORGANS 

It seems to be true in general that when a part once useful is 
no longer used, its doom is sealed. It at once begins to degen- 
erate and its final disappearance seems only a question of time. 
In this way the snake has lost all its limbs ; ^ the whale, its hind 

1 The python still has rudiments of the pelvic bones. 



4IO 



TRANSMISSION 



limbs ; the wings have gone from the apteryx and appear to be 
going from the ostrich ; eyes of cave insects and fishes are in 
many cases imperfect or rudimentary ; horses, cattle, sheep, 
and hogs have lost toes that belonged to their ancestors, and 
parts generally which are functionless are evidently disappearing. 
How, now, are parts lost, when once they have become useless ? 

Economy of Nature not the reason for loss of parts. It is 
sometimes said that a part no longer used is removed by Nature 
in the interest of economy. This is bad science. Nature is not 
economical. She not only supports many expensive and useless 
parts, such as tremendous horns and tusks, but she often pro- 
duces necessary products in wanton profusion, such as pollen 
and fat. Other and deeper causes are at work, — causes more 
rationally connected with the facts of life, — than any such 
anthropomorphic reason as economy. Whatever may be true 
as to economy of growth, it is a fact, not a principle ; a result, 
not a cause. 

How parts disappear. We are reasonably intelligent upon a 
part of the process of degeneracy and disappearance, at least in 
the more active portions of the body. As long as a part is in 
use, its constant movements increase the flow of blood to that 
part and it enjoys the extreme development that comes only with 
maximum nourishment and uniform healthy exercise. When, 
however, the part is no longer used, the flow of blood is lessened 
and it suffers from lessened nourishment. In this way the first 
steps of degeneration are easily accounted for. 

If the part has been useful heretofore, it has of course been 
sustained by selection. Being no longer useful, this influence is 
withdrawn, and breeding is henceforth totally without reference 
to this particular part; that is to say, there is absolute " cessa- 
tion of selection," or panmixia,^ as to this part. Under this con- 
dition the average parentage would be lower than heretofore, thus 
accounting for a ?,X.\\\ farther step in the downward process. 

To all this is often added the adverse effect of selection, 
when for any reason that influence is turned against the part. 
This "reversal of selection" of course comes only when a part 
once useful has become not merely useless but detrimental. In 

1 Romanes, Darwin and After Darwin, II, 97-100, 291-306. 



TRANSMISSION OF MODIFICATIONS 411 

such event there ensues a third stage of degeneracy. Obviously 
the full effects of selection will depend very much upon the 
character of the part and its connection with the vital interests 
of the species. 

The influences just mentioned will sufficiently account for ex- 
treme degeneracy of a once active part, but they will not account 
for absolute disappeaj'ancc. Any character under such conditions 
would decrease to a low minimum where its presence becomes 
insignificant, and there it would remain, but it would not abso- 
lutely disappear except through some other agency. That 
characters, even those which were once important, do entirely 
disappear, leaving not even rudimentary parts, is evidenced by 
the disappearance of the legs of snakes, but that the later stages 
are extremely slow is shown by the rudimentary leg bones of 
the python and the whale. 

Degeneration of eyes in cave-dwelling and deep-sea species. 
It is a well-known fact that the eyes of cave fishes and insects 
often exhibit all grades of degeneration, from near the normal 
down to the merest rudiments. Being entirely useless under 
the conditions of life, selection is suspended, and Nature is 
having her way with the remnants of what was once a highly 
developed organ. 

Deep-sea fishes are either in the same condition or else are 
supplied with enormous eyes of a kind evidently fitted to per- 
ceive light rather than to make distinct and clear-cut images. 

The gradual failure of parts like the toes that have gone from 
the horse, or the apparently disappearing vermiform appendix, 
might be attributed to some failure or imperfection in the germ ; 
but the instance of disappearing limbs is too clearly connected 
with disuse, and that of disappearing eyes with lack of what 
may be called essential conditions of development, to be explained 
wholly on the ground of imperfection from within as the funda- 
mental cause of degeneracy.^ 

The final disappearance of a useless part is certainly due to 
some fact other than the withdrawal or even the reversal of 
selection. There must be morphological units of some kind 

1 Light is evidently essential to the origin of the sensitive spot we call the eye, 
especially in the formation of pigment. 



412 



TRANSMISSION 



resident within the germ, from which they slowly disappear 
when no longer favored by the conditions of life and no longer 
sustained by selection. These vital units, if ever discovered, will 
be found to be closely connected with the origin of characters 
as well as with their preservation. 

We shall see later that, zvhen a character is undergoing rigor- 
ons selection new and Jiighcr values than ever before are constantly 
appearing. May not the reverse be also true, — namely, that a 
character on the decline may present its successive decreasing 
values because of influences entirely internal .'' 

That disappearance of parts is not due entirely to disuse is 
shown by the fact that the process continues long after the fact 
of disuse could have the slightest influence. Where a rudi- 
mentary tibia further degenerates to a rudimentary pelvic bone, 
the question of disuse is certainly not involved ; neither is use 
or disuse involved in breeding for high or low oil in corn, for 
example. Manifestly some biological principle is involved that 
has not yet been discovered and identified, and, as it is evidently 
a principle fundamental to transmission and variation, its isola- 
tion is exceedingly important. 

Characters not dependent upon adaptation. Generally speak- 
ing, there is a close correlation between the development of a 
character and its usefulness to the individual and the species.^, 
This fact has given rise to the impression that all characters 
are dependent upon teleological principles for their existence. 
No greater error could be made. It is true that in nature selec- 
tion operates mostly along utilitarian lines, and in this way after 
a time it brings most characters into line with the greatest 
service and the closest adaptation; but selection may operate in 
any direction, even to the disadvantage of a species. In this 
case, however, the response is to selection, not to utility. 

Neither is development along utilitarian lines necessarily 
true of those characters that lie outside the field of selection 
or of those upon which it operates too rarely to impress itself. 
For example, the instinct to fly toward a source of light 
would exterminate certain species if naked fire were more gener- 
ally encountered. That the testicle in mammals should have 
1 Known among biologists as teleology. 



TRANSMISSION OF MODIFICATIONS 413 

descended into an external sac (the scrotum) is in no way use- 
ful ; on the contrary, it is in many ways unfortunate for the 
individual. Again, the extreme development of the testes in 
cattle, and especially in sheep, is most inconvenient, not to say 
dangerous. Such unusual size is in no way necessary, as we 
must infer from comparison with other species. It is one of 
the strange overgrowths of nature, unfortunate, but not suffi- 
ciently dangerous to destroy the species. In other words, here 
are characters upon which selection has never fastened its hold, 
and consequently they have not been made to square with the 
highest degree of utility, and have not been brought into the 
closest " fit." The inference is unavoidable that the existence 
of a character is not absolutely dependent upon its usefulness.^ 
All this is matter of slight consequence in itself, but it is of 
fundamental importance when discussing questions touching the 
disappearance of characters and the transmission of variations. 

The origin of characters. Considerations such as here engage 
the attention, impel the student to raise, in his own mind at 
least, the ultimate question. What was the origin of racial 
characters, and how did they come into being ? 

It may be humiliating, but it is certainly necessary, to say 
that we do not know, and to freely confess that present informa- 
tion throws little light upon the question. The Lamarckians 
find a ready answer in asserting that all characters have origi- 
nated in the necessities of the individual and the race, and in 
the influence of the conditions of life ; but it is both illogical 
and unscientific to assume that an organ or a part " arose " for 
no greater reason than that the need for it existed. 

The opponents of the Lamarckians, — among whom Weis- 
mann is the recognized leader, — depending as they do exclu- 
sively upon selection, must assume the preexistence of the 
characters on which selection may operate, for selection as such 
can originate nothing; but this introduces new difficulties, for all 
higher life is cdhsidered to have ev^olved from lower through the 
acquisition of characters leading to greater specialization. Now 
these differentiating characters must have arisen sometime, some- 
where, and in some way. Weismann recognizes this difficulty and 

^ Of what possible use is the "beard" on the breast of the turkey? 



414 



TRANSMISSION 



meets it by assuming that the characters that distinguish the higher 
races were in some way impressed upon the original protoplasm 
from without, ivhile the remote ancestors were yet in the single- 
celled stage. Thus do the most radical " selectionists " become 
Lamarckians of the purest kind when driven far enough back.^ 

But is this violent assumption necessary ? Life in the single- 
celled stage is not f?indament ally di^&rQwi from life in the colony 
form. A cell is a cell in either case, and its activity — what it 
can do — is dependent partly upon its ancestry and partly upon 
the conditions of life, which are its opportunities. To be sure, 
the single cell is more dependent upon the external world, and 
reacts more completely to temperature and other external forces, 
than does the larger colony of highly specialized units (cells), 
but this is a difference in degree rather than in kind. 

In the last analysis we are driven to the conclusion either 
that all characters were created and implanted in the original 
protoplasm, — so that living matter, even in its simplest form, 
has all the potentialities of the highest form of life, — or else 
that the peculiar chemical compounds that constitute living mat- 
ter are able not only to enter into definite relations with the 
world at large, but also, perhaps, to effect, from time to time, 
new combinations among themselves, thus acquiring new or 
greatly modified characters, sometimes conforming naturally to 
surrounding conditions, sometimes not. To this latter view the 
writer strongly inclines. 

A chemical element, as iron, acquires no new characters, 
though it behaves differently under different circumstances. 
Sulphur is extremely sensitive to surrounding conditions, and 
many of the organic compounds depend almost entirely for their 
properties upon the conditions under which their peculiar com- 
binations were effected. 

But when life enters the field all the complications are infi- 
nitely multiplied, and when we are driven to the last ditch all 
must agree that the characters possessed by living matter are 
to a large extent and in some way an expression of the condi- 
tions of life. How these conditions impress themselves not only 
upon the individual but also upon the race is, in some cases at 

1 Weismann, Germ Plasm, pp. 415-416. 



TRANSMISSION OF MODIFICATIONS 415 

least (temperature, food, poisons, and many chemicals not 
poisons), both evident and easy to understand ; in others it is 
obscure and uncertain to the last degree. 

Degeneracy and origin contrasted. Of one thing we are cer- 
tain : characters are disappearing before our very eyes, and 
whole races are becoming extinct. What does this mean .? Is the 
world growing poorer in possibilities ? Is specialization realized 
only at the expense of lessened adaptability to new conditions 
later on .? If a part or a character now useless degenerates and 
disappears will it ever come back, or will a new one arise to take 
its place if necessity for its presence should return .? 

These are large questions — questions that we cannot answer, 
but that we must think about and take into consideration in the 
studying and answering of easier and smaller questions. 

In the meantime we will remember that soles, flounders, and 
the flatfishes generally are developing a new style of living,^ and 
that their eyes are taking a new position with reference to the 
other body parts. We will not forget that all animals that live 
in (under) the water, if of much size, are of one general shape, 
— the shape of least resistance to water. That this is independ- 
ent of selection is shown in the history of the whale and of the 
few land mammals that took to the water and whose transforma- 
tion must have been comparatively recent. 

We will remember that, while most " new characters " are 
but new combinations and different adjustments of old ones, 
there is, after all, progressive development showing the infusion 
of something practically new and different. Higher life differs 
from lower in kind as well as in degree. That it springs from 
the lower is certain, and that something has been added in the 
process is no less certain. 

The world is full of lowly forms of life. The species of single- 
celled organisms that are known probably far outnumber existing 

^ These fishes, of which there are a number of species, are symmetrical, or 
nearly so, in the embiyo and for a Httle time afterward, so that at first they swim 
like any other fish. The swimming bladder is defective, however, and shortly they 
tjrn to one side and lie on the bottom, generally left side down, — though some 
individuals are reversed. In this position the left (now lower) eye travels upward 
toward the other side, until the two eyes lie side by side on the right, now the 
upper, side. 



4i6 TRANSMISSION 

species of highly developed organisms. Is this the " raw mate- 
rial " out of which new species shall be evolved later on to take 
the place of what is now so rapidly becoming extinct ? It is a 
moving panorama, and we know neither the beginning nor the 
end. It is all a part of a vast plan on which the universe is 
founded by the Creator. We cannot doubt that the most com- 
plex element of it all is life, nor can we doubt that the most 
characteristic property of living matter is \X^ prog7'essive devel- 
opment, bringing to light new activities and establishing new 
relations with the world outside. Whether this property is wholly 
internal and dynamic, or due, at least to some extent, to outside 
influences, — this is the chief mystery. 

SECTION IX — VARIATIONS DUE TO CAUSES NOT AFFECT- 
ING THE GERM ARE NOT TRANSMITTED 

This much is a logical conclusion. This much is fundamental 
and axiomatic. The germinal matter is the only material that 
passes over from generation to generation. The fertilized germ 
is the only heritage, and it is the only avenue of transmission. 
Whatever faculties or endowments the individual may possess, 
he can transmit only those which can find lodgment and repre- 
sentation in the germ, and whether the causes of germinal 
changes are internal or external, or both, no variation can be 
transmitted unless it affects the germ or unless the cause that 
induced the variation also affected the germ. 

Variations due to causes internal to the body but external to 
the germ are not transmitted. It is entirely possible that certain 
variations, either of structure or of function, may arise from 
irregularities in cell division during development due to local 
rather than to germinal causes. For example, it has already 
been noted that cells may at any time divide into unequal por- 
tions, or into three instead of two parts, giving rise to abnormal 
if not to pathological conditions. 

Almost all portions of the body are subject to those over- 
growths called tumors, and while it is not yet definitely known 
whether the causes of abnormal growth are external or internal 
to the organism, they certainly are not located in the germ. 



TRANSMISSION OF MODIFICATIONS 417 

The probability is that they are entirely local, sometimes arising 
from external injuries, as in galls, and thus outside the present 
field of inquiry, but more often due to internal disturbances in 
the cells themselves at the particular point where the abnormal 
functioning appears. 

Modifications due to external causes sometimes transmitted, 
oftener not. The effects of such all-pervading influences as 
nourishment, temperature, chemical action, gravity, etc., are 
not felt simply by the external parts, but on the contrary they 
may extend to the innermost parts of the organism, affecting 
the constitution and the activities of the most highly specialized 
matter, extending, for all we know, to the very germ, in which 
case they would certainly be transmitted, whereas there is no 
ground for belief in the transmission of influences that do not 
affect the germ. 

Summary. When we speak of the transmission of a modifi- 
cation we mean rather the transmission of a character as modi- 
fied. Strictly speaking, a character will be transmitted in a 
modified form if the modification affects the germ ; otherwise it 
will be transmitted in an unmodified form, for the germ is the 
only hereditary substance, and nothing is transmitted except 
through the germ. 

A modification may arise from causes either internal or exter- 
nal to the germ. If internal it of necessity affects the germ and 
is transmitted. This is the ordinary cause of hereditary varia- 
bility. If, on the other hand, the modification arose from external 
causes, the germ may or may not be affected, and- the modifica- 
tion may or may not be transmitted. 

There is much reason to believe that many modifications of 
functional activity are of such a fundamental nature as to influ- 
ence the germ as well as the soma, and such modifications 
would be transmitted and inherited by the offspring. 

/;/ general, the great effect of the environment is to infinence 
development, not to induce new characters. The environment 
does not decide what characters shall compose the individual, 
— that is a matter of straight inheritance, — but it does decide 
to a very large extent what degree of development the various 
racial characters shall attain in particular individuals. The 



4i8 TRANSMISSION 

question whether extreme development tends to affect the germ 
and to become inherited is a question beset with many difficul- 
ties. The greatest obstacle to this study is the ever-present 
fact of selection, which rapidly brings about a close correspond- 
ence between organisms and their surroundings. No reliable 
conclusion can be drawn until this influence is accounted for 
or eliminated. 

In further pursuance of this study we now pass to more def- 
inite discriminations as to type and to more exact and critical 
distinctions concerning variability as expressed not in individuals 
but in numbers sufficiently large to be fairly indicative of the race. 

ADDITIONAL REFERENCES 

An Examination of Weismannism. By G. J. Romanes, i vol. 
Darwin and After Darwin. By G. J. Romanes. 2 vols. 
Development and Evolution. By J. M. Baldwin. Science, XVI, 

819-821. 
Environment and its Effect on the Transmitting Power of 

Seeds. By W. W. Tracy. Science, XIX, 738-740. 
Experimental Zoology. By T. H. Morgan. Chapters IV and V, pp. 

43-61. 
Foundations of Zoology. By W. K. Brooks, i vol. 
Heredity and Instinct. By J. M. Baldwin. Science, III, 439-441, 

558-559- 
Inheritance of Acquired Characters. ByE.D. Cope. Science, V, 

633-634 ; by John McFarland, Ibid., 935-945. 

Inheritance of Acquired Characters. (Examples.) By F. H. Her- 
rick. Science, VII, 280. 

Inheritance of Acquired Characters. By D. E. Hutchens (1904). 
Nature, LXXI, 83. 

Nature of Cancers and Abnormal Growths, and Transmissibility 
of Same. By E. B. Bashford. Proceedings of the Royal Society, 
London, LXXI 1 1, 66-67. 

Right- and Left-Eyedness. By G. M.Gould. Science, XIX, 591-594. 

The Heredity of Acquired Characters. Boston Medical and Surgi- 
cal Journal, CXXXVII, 427-428. 

Use-Inheritance. Direction of Hair in Man and Animals and its Appli- 
cation to Darwinism. By W. Kidd. Science, XV, 142-143; also in 
Science, XX, 401-407. 



CHAPTER XII 

TYPE AND VARIABILITY 1 

Enough has been shown in earlier chapters to convince the 
student that variability is an inevitable accompaniment of both 
reproduction and development, and therefore that variation is to 
be expected among living beings everywhere. 

Before anything like a comprehensive idea of transmission 
can be developed therefore, it is necessary to study, not indi- 
viduals, but groups, and to establish definite conceptions as to 
type and variability. In this, as in any other critical study of a 
race, we proceed character by character, and are careful to 
include enough individuals to be fairly representative of the race 
as a whole. 2 

A farmer plants an ear of corn say ten inches in length. 
What he gets is not a crop of ears all ten inches long, but a 
group of ears ranging in length all the way from perhaps three 
or four inches up to eleven or twelve, or even a little more. The 
same principle will hold if the ear that is planted is nine inches 
long instead of ten, except that the distribution will be different, 
lengths running, in general, slightly lower; that is to say, the 
length of ear of the offspring is not the same as that of the 
parent, but it constitutes a " distribution " extending both above 
and below that length. So far as is known, this principle of trans- 
mission holds true in all races and for all characters. Stated in 
more general terms, we may say that the offspring as a wJiole is 
not the same as the immediate parents, but that it constitutes a 
distribution extending from near the lozvcr to approximately the 
upper limits of the race. This suggests at once the idea of type 
and that deviation from type ivJiicJi zve call variability. 

^ 'i^Q Bulletin A\i. iig, Agricultural Experiment Station, University of Illinois, 
by the author of this text. 

'■^ Having discovered the type as to several important characters, it would then 
be possible to select a typical individual. 

419 



420 



TRANSMISSION 



SECTION I— TYPE 



What now is our conception of type ? If ten-inch ears will 
not produce ten-inch ears, but something else, and not only 
something else but a considerable variety of lengths ; and if 
what we get extends both above and below the parent, then we 
arrive at once at a double conception as to type ; that is to say, 
the type of the offspring is not the same as that of the parent. 
The type of the parent is very definite, representing an ideal ; 
but if the offspring is distributed both above and below that 
ideal, some being better and some not so good, then a close 
analysis of the real character of that offspring becomes necessary 
in order to make any just comparison between the two, or to 
arrive at any adequate conception of type in a mixed population, 
even in one arising from a selected ancestry. 

A concrete case will serve best to illustrate the principle 
involved. In the year 1906 some Leaming corn was raised on 
good ground from seed ears exactly ten inches in length. A 
random sample^ of this crop, consisting of 327 ears, gave the 
following distribution as to length : 

One ear was 3.0 inches long, one was 4.0 inches, two were 
5.0 inches, three were 5.5 inches, nine were 6.0 inches, eight 
were 6.5 inches, twelve were 7.0 inches, nineteen were 7.5 
inches, thirty-two were 8.0 inches, forty were 8.5 inches, 
sixty -seven were 9.0 inches, sixty-three were 9.5 inches, 
thirty-eight were 10 inches, twenty-one were 10.5 inches, eight 
were ii.o inches, two were 11.5 inches, and one was 12.0 
inches long.'^ 

1 By a " random sample " is meant a sufficient portion of the whole, taken so 
much at random as to fairly represent the entire crop, or "population," as the 
technical phrase goes. 

2 Measurements might be taken at quarter inches with a seemingly higher 
degree of accuracy, but repeated trials show that the same final results follow 
whether measurements are taken at the quarter inch or at the half inch. The main 
point is that the numbers shall be sufficient and that the sample shall be repre- 
sentative. Judgment must dictate as to the accuracy of the sample, but the num- 
ber depends upon the degree of reliability desired. This matter will be fully 
discussed under the subject of probable error, but experience shows that in studies 
with corn excellent results can be had with from 200 to 300 ears, and very fair 
results may generally be had with half that number. 



TYPE AND VARIABILITY 42 I 

Put in tabular form as it appears in actual work we have the 
following : ^ 



Length of Ears, 
or Value, — t^ 

an / 


No. of Ears, or 
Frequency, — / 

1 


3.5 




n 


4.0 


/ 


1 


4.5 







5.0 


// 


2 


5.5 


/// 


9. 


6.0 


/w//// 


9 


6.5 


M/// 


R 


7.0 


MM// 


12 


7.5 


M M M //// 


10 


8.0 


MMMMMM// 


^2 


8.5 


M M M M M M M M 


40 


9.0 


M M M //// M M M m M M M M M // 


fi7 


9.5 


M M M M M m M M M M M M /// 


fia 


10.0 


M M M M M M M /// 


?SK 


10.5 


M M M M / 


21 


11.0 


M/// 


8 


11.5 


// 


2 


12. 0_ 


/ 


1 



Here we have a "frequency distribution" representing the 
entire "population," or crop, and as it lies spread out before 
the eye a glance is sufHcient to afford considerable information 
as to the prevailing type. 

It will be noted at once that there are more ears of 9 inches 
than of any other length, and that the distribution decreases in 
both directions, but unequally, from this highest frequency. 

The mode. This highest frequency, or most common length, 
shows clearly what is the prevailing type in the crop, as distinct 
from the selective type of 10 inches in the seed ear, and it is 
held by statisticians and by students generally to be the best 
obtainable single expression for type. When it is ascertained, 

1 This is the most convenient form in which to make the original record. A 
mark is made for every individual examined, and the additions are readily made. 



422 



TRANSMISSION 



therefore, we know at once wJiat is the natural type^ of tJie race 
or variety so far as the character in question is concerned, and 
wJic7i this is dctennined for a ninnber of iuiportant characters ive 
shall have a good knoivledge of the racial type as a ivJiole. Thus 
we might obtain the mode for circumference, number of rows, 
weight of ear, color of grain, per cent of cob, or any other desired 
character, and having done so a typical ear of this variety could 
be definitely described. We thus arrive at an accurate idea of 
type in a general population, and of its definite measurement. 

The empirical and the theoretical mode. It is evident by in- 
spection of the frequency table that if measurements had been 
taken at the quarter inch, or some less fraction, the highest fre- 
quency would have fallen not at the nine-inch point but slightly 
above it, for the next frequency above {6^) is greater than the 
next one below (40) ; that is to say, the mode is to some slight 
extent dependent upon the scheme of measurements adopted. 

Any scheme expressed in numbers, either whole or fractional, 
is of course by nature discontinuous, and the mode arising from 
such a scheme is at best only an approximation. It is therefore 
called the empirical mode. If all possible values were repre- 
sented, however, as is done whenever the theoretical curve is 
plotted corresponding to the frequency distribution, such a con- 
tinuous curve will find the true or, as it is called, the " theoretical " 
mode. It is necessary to recognize this distinction, although 
in practical breeding operations the empirical mode arising 
from convenient measurements is sufficiently accurate. 

The coefficient of mode, or modal coefficient.^ It is not enough 
simply to determine which value has the highest frequency, 
even though this gives us the type ; we desire to know also 
\N\\-2iX. proportion of all the individuals tends to drop into the type 

1 It is evident that the frequency distribution and, therefore, the type of an 
adult population is something different from that which was born into the race. 
What that may have been we can never know. Many individuals did not survive, 
and the development of all was influenced by environment. The final result as 
represented in adult individuals is all we can consider. 

^ The writer has never seen this expression used. It is of little consequence in 
general evolution, but is of much significance in thremmatology, where the 
breeder desires to know what proportion of his animals or plants conforin to 
type. I have, therefore, taken the liberty of using it, as here, — " the coefficient 
of mode, or modal coefficient." 



TYPE AND VARIABILITY 423 

of the race. This is easily determined in the form of a rate 
per cent by dividing the highest frequency by the total number 
of variates.^ The highest frequency in this case is 6"] , which is 
over 20 per cent (20.4 +) of the total number of ears measured. 
This we call its modal coefficient because it indicates the per- 
centage of the total population that conforms to type in respect 
to this character. The modal coefficient of some other variety 
might be quite different, showing that a higher proportion of 
one variety may conform to type than of another ; or, what is 
the same thing, that one variety may be more constant and 
truer to type. The modal coefficient, therefore, is an index of 
relative conformity to type, a valuable bit of knowledge for 
purposes of selection. 

Modal coefficient partly dependent upon the scheme of measure- 
ments adopted. If these measurements had been taken to the 
quarter inch there would have been twice as many frequencies 
and each would have been represented by correspondingly fewer 
ears. The highest frequency, therefore, would have been not 67 
but approximately half that number, — 33 or thereabouts, — 
and the modal coefficient would have been not 20 per cent but 
near 10 per cent. This being the case, modal coefficients are not 
directly comparable except when arising from the same system 
of measurements, or after the coefficient has been divided by 
the width of the class ; thus, 20 -f- |- equals 10 -r- \. 

For the purpose of comparing the variability of races we use 
the " coefficient of variability," to be described later. The modal 
coefficient is chiefly valuable for comparing one type with 
another within the race, which is all that is required in ordinary 
breeding. 

Practical value of the frequency distribution, the mode, and 
the modal coefficient. The practical importance of the informa- 
tion afforded by these values must be apparent. By means of 
the frequency distribution the breeder is enabled at any time, 
when he can secure sufficient numbers, to spread out before his 
eyes a good and fair representation of the whole population of 
the variety or race he is breeding, with respect to any character 
which he can measure or accurately estimate. 

1 By vaiiates is meant the individuals measured (in this case 327 ears). 



424 



TRANSMISSION 



When he has ascertained its mode he knows what is the 
natural type, for mode indicates type ; and he then knows by 
how much, if any, it differs from the type ^ which he has chosen 
as the standard for selection. By this he may judge whether 
and to what extent he is operating at variance with nature. 

The mean. There is still another conception of type as to 
this distribution, and that is the average, or " mean " as it is 
technically called. It will be noted that the dis- 
tribution does not decline uniformly both above 
and below the mode ; that is to say, there are 
six values below and only three above, — from 
which we conclude that the average length of ear 
is somewhat different from the most usual length. 
By multiplying each separate length by the num- 
ber of ears of that length and adding the products 
(or, what is the same thing, adding together the 
lengths of all the ears) and then dividing by the 
total number of ears, we find the average, or 
mean length, to be 8.83— inches. 

Accordingly we have the following for the de- 
termination of the mean ^ : Multiply each value 
by its frequency, add the results, and divide the 
sum by the number of individuals ^ or variates. 

Applying this principle to the case in hand we 
have the result seen in the accompanying table : * 

* It is customary to drop off extremely outlying values in 
the distribution, but evidently in this case if very large num- 
bers had been taken these blanks would have been filled ; that is, ears of 3.5 inches 
and 4.5 inches would have been found ; hence all values are included here. 

1 Here is another conception of type. The ideal of the breeder, which he 
accepts as his standard, is a kind of economic or business type, quite distinct 
from the biological type indicated by the mode. The purpose of all breeding is 
to bring the two as close together as possible. 

2 By " mean " is here meant the arithmetical average, which is the average most 
commonly accepted and the symbol of which is M. For a discussion of different 
averages, see Appendi.x. 



V 


/ 


fv* 


3.0 X 


I = 


3-0 


3-5 X 


= 


CO 


4.0 X 


I = 


4.0 


4.5 X 


== 


0.0 


5.0 X 


2 = 


lO.O 


5-5 X 


3 = 


16.5 


6.0 X 


9 = 


54-0 


6.5 X 


8 = 


52.0 


7.0 X 


12 = 


84.0 


7.5 X 


19 = 


142.5 


8.0 X 


32 = 


256.0 


8.5 X 


40 - 


340.0 


9.0 X 


67 = 


603.0 


9.5 X 


63 = 


598-5 


lO.O X 


38 = 


380.0 


10.5 X 


21 = 


220.5 


II. X 


8 = 


88.0 


11.5 X 


2 = 


23.0 


12.0 X 


127 ; 


12.0 


~2 


1887.0 


2887.0-=- 


327= f 


(.83-, 


the mean length of 


ear in inches 



3 The algebraic formula would be M - 



(v^A) + {V2/2) 



(K/,) 



, in which 
n 

V'' the respective values, and n the 



f\i fi. ' ' • />■ ^^re the frequencies, V\, Fo^ 
number of individuals measured. 

* In this table F stands for values, or magnitudes, — in this case length, — 
and / stands for frequency, or the number of varieties (ears) of each separate 
measurement. The whole column under y is technically kaown as a "frequency 



TYPE AND VARIABILITY 



425 



Here we have a third vakiation for type (8.83 — ), represent- 
ing the average, as distinct from 9 of the highest frequency, 
or most usual length, and both distinct from the 10 inches of 
the ear planted. 

Practical use of the mean. The mean gives a good average 
value of the character, and establishes the practical or com- 
mercial value of a race or variety, for it shows what it will do 
on the average. It is not always, however, a good index of the 
prevailing type, for, as often happens, the variety with the 
higher mean may have the lower mode. Neither is the mean 
always a good index of conditions ; for example, in a population 
of one thousand paupers and one millionaire the mean wealth 
is fair, but the type is clearly that of the pauper. 

Here are three separate and very definite conceptions of 
type: (i) the ideal, which is used in selecting the parentage; 
(2) the prevailing type as represented by the highest frequency 
or most usual length (the mode) ; and (3) the average length as 
represented by the mean. 

These three conceptions of type — the ideal type of the 
parent, the prevailing type of the offspring, and the general 
average of the offspring — have distinct applications to the 
practical affairs of breeding.^ The breeder of pedigreed stock 
is interested primarily in the ideal and in the mode, or highest 
frequency, while the general farmer who multiplies or raises it 
for the open market is most interested in its mean, or average 
production. 

SECTION II — VARIABILITY, OR DEVIATION 
FROM TYPE 

Having established definite distinctions as to type, the student 
of transmission should next form equally clear conceptions as to 
deviation from type, commonly known as variability.^ 

distribution," representing an entire race, spoken of as the " population." The 
heading fV means the products of the values (lengths) multiplied by the corre- 
sponding frequencies. 

1 It is to be noted that the generation to which the selected parent belonged 
had also its own mode and mean, which may have been quite different from those 
of the offspring. 

2 The term " variability " should not be understood as expressing departure 
in the sense of wandering from a fixed standard. Students sometimes gain the 



426 TRANSMISSION 

In the study of variability it is worse than useless to study a 
few scattered individuals here and there. What we seek is a 
measure of what may be called the average tendency to deviate 
from type. Some individuals deviate but little, others more, 
and still others very much, and we seek a measure of this non- 
conformity to type. To find this we must study groups of in- 
dividuals sufficiently large to be representative of their race. 
This brings us back to the frequency distribution and what it 
can teach as to variability.^ 

impression that if the law of heredity were infallible all offspring would be of a 
common type, and that any departure from the type of the race, variety, or breed 
is to be regarded as by so much a failure of heredity and a concession to variation. 

The truth is that all transmission is heterogeneous in the sense that the indi- 
viduals of any race, whether parents or offspring, belong not to a fixed type but 
to a frequency distribution similar to the one now under discussion. The idea of 
type thus arises out of the distribution, and it constitutes a convenient base from 
which to reckon deviation. 

The chief conception to rest in the mind of the student at the present stage of 
matters is that, whatever the parentage, the offspring will constitute a distribution 
extending through a considerable range, and that the parent itself also belonged 
and was drawn from some portion of a frequency distribution not very different 
from that of the race in general. 

Variability is, therefore, not the opponent of heredity but its inevitable 
accompaniment in transmission, and our problem is to devise methods of accu- 
rately measuring and expressing its range and extent in any particular instance. 

1 No apology is made for introducing the so-called statistical method of study 
at this point ; first, because it is the only reliable method of attacking problems 
in transmission, and second, because this method is everywhere coming into use 
among careful students. The reader is urged, and the student should be required, 
not to evade this portion of the subject because the method of treatment may 
happen to be unfamiliar. On the other hand, he is urged to familiarize himself 
not only with the method of work but with the point of view involved. If he will 
do this, both variability and later on correlation and heredity in general will come 
to have a new meaning, and one far more rational and comprehensive than the 
hazy notions evolved from the unsystematic study of isolated individuals. The 
principles involved are for the most part simple, and in this elementary treatise 
every effort will be made to treat the subject from the standpoint of the non- 
mathematical reader. 

For the convenience of those who may care to pursue a little further some of 
the more strictly mathematical conceptions involved, an Appendix has been pre- 
pared by Dr. H. L. Rietz, of the mathematical department of the University of 
Illinois. 

The statistical method of study of problems in heredity, as distinct from the 
strictly biological, was introduced jjy Dr. Francis Galton of England (see Natural 
Inheritance, 1889), and afterward much extended by Karl Pearson and others 
(see especially Grammar of Science and Philosophical Transactions of the Royal 
Society). It is now coming into such common use that a quarterly journal 



TYPE AND VARIABILITY 427 

Again the concrete serves well as a medium for teaching a 
principle. In this connection we refer once more to our distri- 
bution of 327 ears, and note that evety ear in tJic lot deviates 
somewhat from the mean of 8.83 inches. The range and extent 
of this deviation are shown in the following table, column D. 

The practical question now is to reduce 

,, • 1 r 1 • -■ . -1 Deviation of 327 Ears 

this column ot deviations to a single ex- ^ ^ ' 

pression denoting the variability of the 
population of which this distribution is 
representative. Manifestly, when this is 
done, the variability of this distribution 
can be compared directly and exactly with 
that of any other, and at the present or 
any future time. Two methods of pro- 
cedure are possible in thus securing a kind 
of general expression for the average 
amount of deviation, giving rise to two 
similar but slightly different values, 
namely, the average deviation and the 
standard deviation. 

The average deviation. If each de\i- 
ation (column D) represented an equal 
number of ears, this single expression 
could be readily derived by adding the 
deviations and dividing by the total 
number. But these deviations do not 
represent equal numbers of ears. The 
deviation —5.83, for example, represents but one ear, while no 
less than twelve ears deviated 1.83 inches below the mean and 
two deviated 2.67 inches above, with others unevenly distributed. 

Manifestly each deviation should first be multiplied by the 
number of ears involved, as in the succeeding table : ^ 

{Biornetrikn) is devoted to the reports of statistical studies in evolution, technically 
known as " biometry." 

1 When the deviation is to be obtained in this way the minus sign is disregarded. 

* D indicates the deviation of the several groups from the common mean of 
the race, 8.83 inches. Thus, for example, the first ear deviates the difference 
between 3 inches and 8.83 inches, or 5.83, which, being below the mean, is written 
with the negative sign ; also the 21 ears 10.5 inches long deviate 10.5 — 8.83, or 1.67 
inches from the mean, and being above the mean, we write it positive. 



OF Corn from their 


Mean Length of 


8.83 


Inches 




V 


/ 


D* 


3-0 


I 


-5-83 


3-5 





- 5-33 


4.0 


I 


-4.S3 


4-5 





- 4-33 


5-0 


2 


-3-83 


5-5 


3 


- 3-33 


6.0 


9 


-2.83 


6.5 


8 


- ^-33 


7.0 


12 


- 1.83 


7-5 


19 


- 1-33 


8.0 


32 


-0.S3 


8-5 


40 


-0.33 


9.0 


67 


0.17 


9-5 


63 


0.67 


lO.O 


38 


1. 17 


10.5 


21 


1.67 


II.O 


8 


2.17 


II-5 


2 


2.67 


12.0 


I 

327 


3-17 



421 



TRANSMISSION 



/ ^ 

I X 5.83 : 

X 5.33 : 

1 X 4-83 = 

X 4-33 '- 

2 X 3.83 : 

3 X 3-33 ■■ 
9 X 2.83 : 

8 X 2.33 : 
12 X 1.83 : 

19 X 1.33: 

32 X 0.83 : 

40 X 0.33 
67 X 0.17 

63 X 0.67 : 

38 X 1. 17 

21 X 1.67 

8 X 2.17 
2 X 2.67 

1 X 3.17 

327 



- 5-83 

: 0.00 

: 4.83 

: 0.00 

= 7.66 

= 9-99 

= 25.47 

: 18.64 

: 21.96 

= 25.27 

= 26.56 

= 13-20 

= 11-39 
= 42.21 
= 44.46 
= 35-07 
= 17-36 
= 5-34 
= 3-17 
318.41 



The result of this calculation is that the 
total deviation of 327 ears from their average 
length is 318.41 inches, some above and some 
below the mean. If now we divide 318.41 by 
327, the number of ears involved, we have 
0.97+ inches, which is a good expression of 
the average deviation of this particular popu- 
lation. If another variety should give a larger 
quotient, we should conclude it to be more 
variable. In this manner we may reduce the 
variability of a whole population to a single 
expression. 

Standard deviation. Mathematicians have 
another method of calculating variability. It 
differs from the one just discussed in only one 
detail ; namely, the deviations ai-e squared 
before multiplication by their respective fre- 
quencies, as in the table which follows : 



V 


/ 


D 


£,1* 


D-/^ 


3-0 


I 


-5-83 


33-9889 


33-9889 


3-5 





- 5-33 


28.4089 


00.0000 


4.0 


I 


-4-83 


23-3289 


23-3289 


4-5 





- 4-33 


18.7489 


00.0000 


5-0 


2 


-3-83 


14.6689 


29-3378 


5-5 


3 


- 3-33 


11.0889 


33-2667 


6.0 


9 f 


-2.83 


8.0089 


72.0801 


6-5 


8 ^ 


- 2.33 


5.4289 


43-4312 


7.0 


12 


-1.83 


3-3489 


40.1868 


7-5 


'9 


- 1-33 


1.7689 


33.6091 


8.0 


32 


-0.83 


0.6889 


22.0448 


8.5 


40 


-0.33 


0.1089 


43560 


9.0 


67 


0.17 


0.0289 


1-9363 


9-5 


63 


0.67 


0.4489 


28.2807 


1 0.0 


38 


1. 17 


1.3689 


52.0182 


10.5 


21 


1.67 


2.7889 


58.5669 


II.O 


8 


2.17 


4.7089 


37.6712 


II. 5 


2 


2.67 


7.1289 


14.2578 


12.0 


I 


3-'7 


10.0489 


10.0489 




327 






S 538.4103 t 



* The column marked D" is secured by squaring the various deviations, thus 
eliminating the minus sign. For example, — 5.83 X — 5.83 = 33.9889. 

t The column marked D-f is obtained by multiplying the squared deviations 
each by its respective frequency. For example, 8.00S9 x 9 = 72.0801. 

t The Greek capital sigma (S) is the usual sign of summation in mathematics. 



TYPE AND VARIABILITY 429 

Dividing 538.4103 by 327 after the manner of finding the 
average deviation, we have the quotient 1.6465 ; but as the 
deviations have all been squared during the operation it is 
necessary to extract the square root of this number in order to 
arrive at the correct value. The square root of 1.6465 is 1.28 +, 
and this is the so-called standard deviation of the mathema- 
tician, the universal sign for which is the Greek letter, small 
sigma (o-). 

Hence, to find the standard deviation, we have the rule : Find 
the deviation of each frequency from the mean ; square each 
deviation, and multiply by its corresponding frequency ; add the 
products, divide by the total number of variates, and extract 
the square root.^ 

Shortening the method. The large decimals can be avoided, 
and the process of finding both the mean and the standard 
deviation can be very much shortened, by assuming' as a mean 
the nearest probable measurement as determined by inspection 
of the frequency distribution, and afterward making a suitable 
correction. For example, in the present instance, we should 
judge by inspection that the mean cannot be far from 9.0.* 
This we infer from the fact that the distribution reduces both 
ways from this point and quite evenly. Proceeding with this 
assumption, denoting our "guess" by G and reckoning devia- 
tion provisionally from this point, we have the result as seen 
in the table on the following page. 

Considering first the mean : In columny"(F— G) we find that 
after multiplying the deviations from our assumed mean (9.0) 
by their respective frequencies, the sum of the negative products 
(— 1 81.0) exceeds the sum of the positive products (125.0) by 
56.0 ; that is, the algebraic sum of the products is — 56.0. 
Our assumed mean is therefore too high by the amount of 
— 56.0 -i- 327! = —0.1 7 1. We then reduce our assumed mean 



—. 



* The advantage of assuming this value from which to reckon deviation Ues in 
the fact that it is exact and contains but one decimal, while the true mean has at 
least two decimal places, making relatively large numbers. 

t We divide by the total number (327) because we are dealing with a column 
of products arising from the introduction of the frequencies. 



430 



TRANSMISSION 



by this amount (9.0 — 0.171=8.829) and arrive at the true 
mean 8.83 — .* 

Considering next the standard deviation : In cokmin/(r— G)'^ 
we have 548.00 as the sum of the products of the several fre- 
quencies into their respective deviations from the assumed mean, 
derived on the same plan as when working from the true mean 



V 


f 


V-G 


/(r-G) 


{V-G)-' 


/{V-GT- 


3-0 


I 


- 6.0 


- 6.0 


36.00 


36.00 


3-5 





- 5-5 


0.0 


30-25 


00.00 


4.0 


I 


- 5-0 


- 5-0 


25.00 


25.00 


4-5 





-4-5 


0.0 


20.25 


00.00 


5.0 


2 


- 4.0 


- 8.0 


16.00 


32.00 


5-5 


3 


- 3-5 


- 10.5 


12.25 


36-75 


6.0 


9 


- 3-0 


- 27.0 


9.00 


81.00 


6-5 


8 


- 2-5 


— 20.0 


6.25 


50.00 


7.0 


12 


— 2.0 


— 24.0 


4.00 


48.00 


7-5 


19 


- 1-5 


-28.5 


2.25 


42-75 


8.0 


32 


— I.O 


-32.0 


1. 00 


32.00 


8.5 


40 


- 0.5 


— 20.0 


0.25 


10.00 


9.0 


67 


0.0 


0.0 — 181. 


0.00 


00.00 


9-5 


63 


0-5 


3'-5 


0.25 


15-75 


1 0.0 


38 


1.0 


38.0 


1. 00 


38.00 


10.5 


21 


1-5 


3'-5 


2.25 


47-25 


II.O 


8 


2.0 


16.0 


4.00 


32.00 


II. 5 


2 


2-5 


5.0 


6.25 


12.50 


12.0 


I 


3-0 


3.0 125.0 


9.00 


9.00 




l^-l 




Difference, — 56.0 




S 548.00 



D. Dividing by the total number (327), we have 548.00 -^ 327 = 
1.6758, corresponding to the quotient 538.4103 -^ 327 = 1.6465 
of the previous calculation when working from the true mean. 

The correction made in the mean was — o. 171 ; but as we are 
now dealing with second powers it seems but natural that this 
amount should be squared before it can be taken from the quo- 
tient 1.6758. This will be justified by a mathematical proof in 
the Appendix. The square of — 0.171 is 0.029241, or 0.0292 +. 

* On the other hand, should the sum of the positive deviations exceed the sum 
of the negative deviations it would indicate that our assumed value is too small 
and we should add the correction in order to arrive at the true mean. 



TYPE AND VARIABILITY 



431 



We have therefore as a correction on account of the true mean 
1.6758 — 0.0292 + = 1.6466. 

This agrees very nearly with the vahie 1.6465 previously 
found, but this shorter method is the more accurate, because 
fewer decimals have been lost. The square root of 1.6466 is 
1.28 +, the standard deviation sought, agreeing perfectly with 
the former value and derived by a very much shorter method. 

The student will note that the difference in the two methods 
is essentially this : in the latter we deal only with deviations , 
while in the former entire values are involved. It is true that 
deviations are taken from an assumed mean, but the correction 
is accurately made, and the whole operation can be carried 
forward not only with smaller numbers but also without the 
loss of decimals necessarily involved in the more direct but far 
more laborious and on the whole less exact method first given. 
The first method is useful for expounding the principles in- 
volved, but the later is far preferable for actual use, not only on 
account of its brevity, but on account of its increased accuracy 
as well. 

Average deviation and standard deviation contrasted. These 
two expressions for variability rest upon the same arithmetical 
principle, but the latter has decided mathematical advantages 
over the former for many purposes and is the one universally 
used by mathematicians. The only advantage in the average 
deviation lies in the simpler calculation, as neither squares nor 
roots are involved. With the shortened method of finding the 
standard deviation, however, this advantage is slight. 

It makes little difference which is used in practice, provided 
the same method is always employed. The results obtained differ 
considerably {0.97+ as compared with 1.28 +). The standard 
deviation is always larger than the average deviation because of 
the squaring of the several deviations. It thus exaggerates the 
wider departures from type as compared with the methods 
employed in finding the average deviation. This being true, 
results obtained by the two processes can never be compared ; 
that is, when dealing with values designed to express variability 
we must always know whether average deviation or standard 
deviation is meant. 



432 



TRANSMISSION 



The breeder may choose either method, but having once 
chosen, all his records must be made in the same way. In- 
asmuch as the standard deviation has distinct mathematical 
advantages over the simple average deviation, and inasmuch as 
it is the one commonly employed in mathematical literature, it 
is the one that will always be employed in this text. When, 
therefore, a measure of variability is mentioned it will be the 
standard deviation and not the average deviation that is meant. ^ 

Meaning of standard deviation. The standard deviation is a 
good measure of variability for the character in question and 
the race involved. It therefore affords a reliable basis for com- 
paring the variability of one race ivitJi that of another as to the 
character under consideration, or of one cJiaracter zvith that of 
anotJier cither in the same or in different races. 

In ascertaining the standard deviation the mean, or average, 
of the race was taken as the basis, and all deviation was reckoned 
from that. It is manifest, however, that if the mode be taken 
as a basis, and deviation reckoned from this, following the same 
methods as for determining the standard deviation, a somewhat 
different value will result. Whenever, as in most cases, the 
mode does not coincide with the mean, this will represent the 
deviation from the prevailing type, which is often of more prac- 
tical importance to the breeder than the deviation just described, 
especially to the breeder who proposes to deal with individuals 
selected with reference not to the mean but to the prevailing 
type. 

In the same manner the breeder may calculate the deviation 
from his own ideal type or standard and in this way assess the 
deviation, not from the present mean or type but from the one 
he hopes to establish. In this way he is able to keep accurately 
informed from year to year as to the progress he is making and 
the degree of success that is following his selections. 

The writer has never seen either of these determinations 
used, but they are especially valuable to the breeder who desires 
to know how a certain variety deviates on the average from its 

1 In the section on " Probability Curve " (Appendix) it will be shown that the 
standard deviation is on the whole preferable from the purely mathematical 
standpoint. 



IVPE AND VARIABILITY 433 

oivn type or even from his standard of selection, as well as to 
know how it deviates from its own mean. 

I have therefore recommended their use, calling the one 
deviation from mode and the other deviation from standard, 
and earnestly suggest their constant employment by the breeder 
as a means of acquainting himself with the true nature of the 
variety he is attempting to improve ; for improvement consists 
often in changing the type as well as in bringing a larger propor- 
tion of the population to conform either to the natural or to the 
accepted standard. ^ To do this he should make these determina- 
tions year by year, and keep the results as a history of the vari- 
ety or breed as it behaves with him under selection. 

Practical meaning of standard deviation. Inasmuch as the 
standard deviation is an index of variability whether from mean 
or from type, it expresses accurately the tendency of the variety 
to wander, so far as the character in question is concerned. It 
affords, therefore, a basis of comparison of one variety with 
another, or ivitJi itself at some future time. However, one 
standard deviation ordinarily cannot be compared di?rctly with 
another for two reasons : first, one mean may be very much 
larger than the other ; and second, the two may be of entirely 
different units, as inches and pounds, in which case direct 
comparison is impossible. 

Coefficient of variability. We seek, therefore, an abstract 
expression combining the idea both of standard deviation and 
of type. Such an expression is known as the " coefficient of vari- 
ability," and is found as follows : Divide the standard deviation 
by the mean as a base, and the result will be an excellent index 
of variability appearing in the form of a rate per cent.^ 

Thus, for the case in question, we have 1.28 -f- 8.83 =0.145, 
indicating the variability of this population to be over 14.5 per 
cent of its own mean. Here we have a mathematical expression 
for comparing variability on a perfectly abstract basis, and by 
this means we can compare the variability of this population 

1 " Standard," as here used, refers to the scale of points, or that which the 

breeder is trying to estabhsh. It is his standard for selection. 

„ _, , , . ^ standard deviation a 

^ The formula is C = or r-^. 

mean M 



434 TRANSMISSION 

with that of any other race, plant or animal, and for any charac- 
ter of which accurate measurements can be taken and a fre- 
quency distribution be constructed.^ 

Practical application of the coefficient of variability. The 
value of this term lies in the fact that it affords an accurate 
means of comparing directly the variability of one frequency 
distribution with that of another, no matter what the character, — 
whctJier in the same or different individuals, or between similar 
or imlike species. Thus, by this means we may compare the vari- 
ability of the length of an ear of corn with that of its weight ; 
the variability of its circumference with that of its number of 
rows, or with that of any other measurable character. 

We can also, in this way, compare the variability of ears of 
corn with that of their stalks ; with that of the length of horse's 
legs, of what they can pull, or of the rate at which they can 
travel ; with that of the height of men, their weight, length of 
arms, measurements of the head, — indeed, with that of any 
object, living or non-living, that possesses variable characters 
that can be accurately measured, whether by feet, inches, 
pounds, or by any other unit that can be devised.^ 

By means of this coefficient the breeder may not only ascertain 
whether one character is more variable than another, but by 
taking this coefficient frequently, as annually for the same variety 
or under different conditions, he can know the variability of the 
same character as influenced by time or circumstances. 

In general these determinations enable the breeder to know 
which way his varieties are drifting, or whether they are standing 

1 Clearly, if the mode or the standard of selection has been used as a base in 
calculating the deviation, then the same value should be used as a base in calcu- 
lating the coefficient ; thus it is possible to secure a coefficient of variability from 
any desired type as well as from the mean. 

^ The coefficient of variability has been worked out for a large number of 
characters in man, as is shown in the following table (see Vernon, Variation in 
Animals and Plants, p. 24). 

Nose length 9.49 Head breadth 2.78 

Nose breadth 7.57 Upper arm length 6.50 

Nose height 15.20 Forearm length 3-85 

Forehead height 10.40 Upper leg length 5.00 

Under jaw length 4.81 Lower leg length 5.04 

Mouth breadth 5.18 Foot length 5.92 

Head length 2.44 



TYPE AND VARIABILITY 



435 



still in spite of vigorous selection ; whether in his selection he 
is operating with or against nature ; whether the type is becom- 
ing a little more " fixed " or whether the tendency is more and 
more to scatter ; whether the mean or general average of excel- 
lence is approaching or receding from the desired type ; whether, 
as time passes, variability is lessened or increased ; whether, as 
the result of selection, neiv values are coming in at the upper 
end. In short, by these calculations he may know whether he is 
making real progress, or is only dabbling in the whirl of vari- 
ability that is inevitable with all living things, without influ- 
encing at all the trend of the race. It is needless to say that 
much of this latter sort of ineffective breeding is going on all 
about us everywhere. The statistical method is the only known 
method of securing accurate knowledge of type and variability ; 
for type is not simply what we desire, but it is what we actually 
get, and any breeder is working in the dark who does not knozv 
the real nature of the zvJiole population of the race he breeds. 

SECTION III — PRACTICAL HINTS ON THE TAKING AND 
GROUPING OF MEASUREMENTS 

It is highly improbable that, in measuring any part of an 
organism, a perfectly accurate measure is obtained. It may be 
very easy to measure the length of an object accurately to i inch, 
or to O.I inch, or even to o.oi inch, if the rule'r is sufficiently 
accurate ; but finally, in trying to measure to as high a degree 
of accuracy as possible, we come to a point where our ruler 
fails us. Again, the object measured may be of such a nature 
that it is futile to try to take measurements beyond a certain 
degree of accuracy. For instance, it would be useless to try to 
measure the length of an ear of corn to o.oi inch. Similarly, in 
weighing substances, it is possible with a good balance to take 
measurements to ounces or to tenths of milligrams if extreme 
accuracy were demanded ; but finally, in striving after accuracy, 
the balance fails us, and we must grant that it is highly improb- 
able that the weight which we record is perfectly accurate. 

While we thus see that we cannot attain absolute accuracy in 
any measurements, yet thremmatology is no exceptional field in 



436 TRANSMISSlOiSl 

this respect, and experience has shown that measurements can be 
easily taken of sufficient accuracy to insure very rehable results. 

For obtaining the frequency distribution of a population with 
respect to some measurable character, it is impracticable to lay 
down specific rules in regard to the accuracy of measurements. 
This must be settled largely by experience and common sense. 
It may, however, be said here that in measuring a large popu- 
lation, under the free action of the laws of probability, substan- 
tially as many measurements will be taken too large as are 
taken too small. Hence slight errors in measurements do not 
appreciably disturb the mean and variability of the population, 
because they tend to offset each other. 

Scheme of measurement. Reverting to the frequency dis- 
tribution obtained from measurements of corn, it will be noted 
that this population is distributed in classes or groups which 
differ by a half inch in length. For the purpose of forming this 
frequency table there would then be no object in taking the 
measurements closer than the nearest half inch. This raises the 
question of the inclusiveness of a class in grouping a population ; 
that is. Should these measurements have been taken at the 
quarter inch or perhaps at the even inch } Here, again, no hard 
and fast rule can be laid down ; but it may be said that in 
general, and for the best results, the class range should be made 
just large enough for some variates to appear in each class, 
except, possibly, in a few near the extremes of the range of 
variability when the total population is not very large. 

Sometimes the best unit for measurement and grouping 
will be evident, but frequently some preliminary work is neces- 
sary in order to decide it. For example, in beginning the 
statistical work with corn we at first took measurements to the 
quarter inch, with groupings accordingly, but found no results 
different, either as to mean or variability, from those obtained 
when measurements were taken to the half inch, and but slightly 
different from those taken at the even inch. Accordingly we 
are using the half-inch measurements for extreme accuracy and 
the even inch for rougher work. 

Much judgment must be used in deciding upon the scheme 
of measurements to be adopted and the groupings to be made. 



TYPE AND VARIABILITY 



437 



If the unit of measurement be large, say two inches for corn, 
the individual values will not be accurate ; the groups will be 
large, but so far apart that the empirical mode will have but 
little meaning. If, on the other hand, the units of measure be 
too minute, say tenths of inches, the work of calculation will 
be vastly increased, and while the empirical mode will be more 
accurate, yet the distribution will not be "smooth," as the 
technical phrase goes ; that is, some of the groups near the 
extremes may not be filled. 

The scheme must be so chosen and the groupings so made as 
to furnish a uniform distribution, with fairly smooth results 
when the frequency is platted in the form of a curve. The 
method of platting frequency distributions and dealing with 
them as " curves of frequency " will be shown in the Appendix.^ 



SECTION IV — PROBABLE ERROR 

Mention has already been made of certain inaccuracies in 
measurements and groupings of a population. Attention is now 
called to another source of error which arises from using a 
limited number to represent the total population. From all 
these sources slight errors are inevitable. We have no means of 
determining the exact error, but after the work has been done we 
may find a measure of accuracy. This measure of accuracy is 
called the " probable error." 

Whatever the source of error, the exact discrepancy in a 
result which depends upon measurements can never be ascer- 
tained. However, the so-called "probable error" does give a 
measure of accuracy which indicates whether we should expect 
a large or small error in a determined value. In other words, it 
indicates the degree of confidence which we should place in 
results obtained by statistical methods. 

1 In general this may be done by laying off the measurements, as inches, half 
inches, pounds, etc., on a horizontal line, and the numbers of individuals in the 
distribution as verticals, connecting the points by a continuous curve. As num- 
bers differ greatly in different cases, it is best to reduce them all to the basis of 
loo, and express all values in percentages. If this is done, then all curves of the 
same measurement are comparable. 



438 TRANSMISSION 

The real nature of probable error and the methods for 
deducing the formulas for its calculation will be covered in 
the Appendix, which is devoted especially to mathematical 
methods and conceptions, but enough should here be said to 
give the student an intelligent idea of what is meant by probable 
error and to acquaint him with the bare formulas for its calcu- 
lation as to the values here under discussion. 

The probable error (denoted by ± ^) is a pair of divergencies 
lying one above and the other below the value determined, and 
of which we can say with confidence that there is an even chance 
that the true value lies between these limits.^ These numbers 
are numerically equal, but one is regarded as plus, the other as 
minus (±^5), and the two define a range within which, out of a 
very large number of determinations, at least half the true values 
would be found. This being the case, we may say of any single 
determination that the chances are even that any error involved 
will not fall outside the limits set by ± E. It is obvious, there- 
fore, that the smaller the probable error the narrower this range, 
the greater confidence we should place in our determination, and 
the smaller are the chances of a large error having been made. 

The expression "probable error" may be misleading. It is 
not, as might be supposed from the words, the most probable 
error. The most probable value is our determination and the 
most probable error is sero. Neither does the probable error 
fix the limits of error, but it is an extremely good measure of 
accuracy in that it fixes a range above and below the determined 
value such that the cJiances are even that the true value lies 
witJiin this range. 

Thus, if a series of calculations results in a final number 27.4, 
with a probable error of ±.12, it means that out of a great 
number of cases the true value of one half will lie between 
27.52 (27.4 + .12) and 27.28 (27.4 — .12). 

If another calculation involving larger numbers or more ac- 
curate methods should result in the same value, 27.4, but a 
probable error of only ± .04, then the true value has an even 
chance of lying between 27.44 and 27.36, which is a very 

1 There is, of course, also an even chance that the true value lies outside the 
same limits. 



TYPE AND VARIABILITY 



439 



narrow margin, giving us much confidence in the determination, 
with only a small chance of being wide of the truth. 

Of course the error in a determination has also an even 
chance of lying outside the limits set by the probable error {E), 
but the following table will show that it is very unlikely that 
the error is many times as great as E. Thus the chances that 
the true value lies within the range set by ±^, ± 2 E, etc., are 
as follows : ^ 

± E the chances are even 
± 2 £" the chances are 4.5 to i 
± 3 £" the chances are 21 to i 
± 4 if the chances are 142 to i 
± 5 iT the chances are 1310 to i 
± 6 is" the chances are 19,200 to 1 
± 7 -£" the chances are 420,000 to i 
± 8 iT the chances are 17,000,000 to i 
± g iT the chances are about 1,000,000,000 to i 

It is extremely improbable, therefore, that an error will be 
many times as large as the probable error. For instance, it is 
practically certain that the error is not as large as 9 E^ since 
the table shows that the chances are about a billion to one in 
favor of its being smaller than 9 E.. 

Thus by giving, along with any result, the calculated /nV;^?/;/? 
error, the reader may know what degree of confidence is to be 
placed in the results. 

For a graphic illustration of the meaning of ± E, suppose in 
the following figure the line AB represents our determination, 
and the lines ab and a'b' the location of + ^ and —E 

A , 
a a 



b 



B 



b^ 



Now this means that if AB is not the true location of the value 
in question, the chances are even that this location is not outside 
the limits set by the lines ab and ^7/ representing ± E. 

1 C. B. Davenport, Statistical Methods, p. 14. 



440 TRANSMISSION 

If now we set other lines like the following at ± 2 E, 



/>i b B // b^ 

then we know from the table that the chances are 4.5 to i 
that the true position of AB is not outside the lines a^b^ and aH"^, 
each removed twice the probable error from the determination. 
Probable error of mean. The probable error of the mean is 
based upon the standard deviation, as we notice by the following 
formula : standard deviation 

^mean = ± O.6745 / . 

V number of variates 
or ^.v= ±0.6745 -^• 

Substituting for the case in hand, we have 

^8.83- = ± 0.6745 -i= = ± 0.047 +• 
V327 

The student cannot fail to notice the overwhelming influence 
of numbers in controlling the value of E^ or to realize that if 
the number of determinations should become infinite, E would 
become zero. 

Probable error of standard deviation. According to methods 
of deduction, to be discussed later, the probable error of any 
determination for standard deviation is found by the follow- 
ing process : divide the standard deviation by the square root 
of twice the number of variates and multiply the result by 
±0.6745.2 

In the case in point we have 1.28 as the standard deviation 
with 327 variates. Substituting these numbers in the formula, 

we have ^28 

^,..8 = ± 0.6745 , = ± 0.034 -. 

V2 X 327 

1 See C. B. Davenport, Statistical Methods, p. 15. The method by which the 
constant 0.6745 ^-'^ obtained will be explained in the Appendix. 
- The formula for probable error of standard deviation is 

Ea = ± 0.6745 . • 

See C. B. Davenport, Statistical Methods, p. 16. 



TYPE AND VARIABILITY 44 1 

If another distribution should give a smaller E, we should con- 
clude that more confidence could be reposed in this second 
determination than in the first. 

Obviously ± E will decrease as the standard deviation de- 
creases or as the numbers examined increase (see formula). Our 
numbers are relatively small (327) and our probable error is 
relatively high, though it constitutes but an insignificant frac- 
tion of the determination (1.28). 

Probable error of coefficient of variability. When the coeffi- 
cient of variability (C) is small (10 per cent or less) its probable 
error is found by dividing the coefficient of variability by the 
square root of twice the number of variates and multiplying by 
±0.6745 ; that is, by the same formula as the one just given, 
only substituting coefficient of variability for standard devia- 
tion.i When the coefficient is larger than 10 per cent we use 
a slightly more complicated formula.^ 

Since the variability in question (14.5) is greater than 10 per 
cent we employ the more extended formula and obtain the 
following : 



^,= ±0.6745 '^'^ 



V 



2 X 327 



, , 14-5 

1 + 2 

100 



±0.39 -f , 



The student will find on trial that for these values the two 
methods give results but slightly different. 

Deviation and probable error illustrated. This whole matter 
of deviation and probable error is well illustrated in shooting 
at a mark. Some of the shots will strike the bull's-eye and 
others will strike at various distances from the center, some 
going wild. Obviously the better the shooting the closer will 
the shots be clustered about the bull's-eye. The distance of 
each shot from the center would be its deviation from the 
mark and the mean of aU the deviations of the marksman A 
would represent the average of his deviations. 



1 Formula Ec — ± 0.6745 —=^ ■ 

V 2« 



^£c=± 0.6745 -^ 



Methods, p. 16. 



C 
100 



See C. B. Davenport, Statistical 



442 



TRANSMISSION 



If a circle be drawn about the center with a radius equal to 
the average deviation of A, this circle will fairly well represent 
his marksmanship ; that is to say, the average distance of all his 
shots from the center is the same as if they all lay on this circle. 
If the marksmanship of B is not so good as that of A, his average 
is greater and the circle correspondingly larger.^ 

Now neither of these circles is an absolute index of the marks- 
manship of either A or B, unless an infinite number of shots 
has been made ; that is to say, if only a few shots have been 
fired, the probability of error is great if we assume these circles 
to be fully representative of the marksmanship, because there 
is practical certainty that succeeding shots will be either better 
or worse ; indeed, there is always a chance that the next may be 
a lucky shot and lower the deviation, or a wild one and raise it. 

We should therefore conceive of two other circles lying 
neighbor to each of those representing the calculated deviations. 
These are represented in the cut by the Hght-Hne circles and 
give a graphic meaning to the probable error. They are drawn 
so that if the heavy circles do not accurately represent A's and 
B's marksmanship then the chances are even that the true 
position of the circle representing A's marksmanship, for exam- 
ple, lies somewhere between the light lines representing the 
probable error of the computation. The chances are of course 
also even that it lies beyond \\\q.'s>q limits, either within or outside. 
Obviously, the smaller the probable error the greater the confi- 
dence to be placed in the calculated deviation. The student is 
cautioned here that in this illustration the " probable error " 
refers not to A's or B's failure to hit the target, but to our 

^ The question may be raised as to whether there is not a better measure of 
marksmanship than the average departure of the shots from the bull's-eye. For 
instance, with the bull's-eye as a center, we may describe circles through each of 
the shots of A, and construct a circle with the average area of these circles for 
its 'area. This circle may then be selected as a measure of A's marksmanship 
instead of the circle above discussed. The radius of this circle can be obtained 
by taking the square root of the mean square of the deviations from the bull's- 
eye. It is not important for us to discuss here the relative merits of these two 
methods of measuring marksmanship, but it is important that we recognize that 
the method explained in the text is based upon what we may well call " average 
deviation from an ideal," while that suggested in this footnote may well be called 
" standard deviation from an ideal." 



TYPE AND VARIABILITY 



443 



■peA 




calculation in assuming the circles to represent the deviation of 
each, when only a limited number of shots had been fired. 

It is this deviation and not our probable error that is to be 
taken as expressing error in marksmanship, for with an infinite 
number of shots our E would disappear, but the error in marks- 
manship or the deviation of A or B would never disappear. With 
infinity it would have an exact and fixed value, with E = o. 

It is obvious that the deviations above alluded to are devia- 
tions from an " ideal " (the center of the target) which is compar- 
able to the selection type in practi- 
cal breeding. It is obvious, too, 
that these heavy circles represent 
the means of all the shots fired by 
the two marksmen, but they do not 
represent their distribution. That 
is to say, A, for example, might 
have put most of his shots, or all 
of them for that matter, at a uni- 
form distance from the bull's-eye, 
none hitting the center and none 
going wild ; in other words, his 
shooting might have been very 
uniform, but neither very good 
nor very bad, owing either to bad 
marksmanship or to a badly sighted 
gun. Now it is conceivable that 
another marksman, C, should succeed in making an average 
identical with that of A, but in a very different manner, — some 
of the shots hitting the bull's-eye and some going wild. These 
two men, then, do shooting of an entirely different class the one 
from the other, that is, make a very different distribution even 
though they win the same mean. If now, from this mean (repre- 
sented by the heavy circles), we calculate standard deviation 
with respect to all the shots fired, we then have a conception of 
deviation corresponding exactly to that of the ordinary standard 
deviation ; namely, deviation from the mean of all the variates. 
Thus we illustrate both deviation from mean and deviation from 
an ideal, together with the probable error involved. 



■pcB 



Fig. 44. Let the heavy lines A and 
B represent the calculated marks- 
manship of A and B respectively ; 
then the light lines peA and peB 
will represent the probable errors 
in the assumption that lines A and 
B represent truly the marksman- 
ship of A and B 



444 



TRANSMISSION 



SECTION V — COMPARATIVE TYPE AND VARIABILITY 

FOR DIFFERENT CHARACTERS IN THE SAME 

POPULATION 

If a variety of characters in the same population be critically 
studied it will be found that each has its own type and variability. 
For example, in the population arising from the ten-inch ears 
already discussed it was found that other characters varied as 
follows : 

Type and Variability for Four Characters of Corn grown from 
Seed Ears Ten Inches Long 



Length of ear . . . 
Circumference of ear 
Weight of ear . . 
Number of rows . . 



Mean, Inches 
OR Ounces 



8.829 ± 0.048 
7.047 ± 0.021 
12.75 ±0.12 
20.09 ± o. I I 



Standard Devia- 
tion, Inches or 
Ounces 



1.283 ± 0.034 
0.568 ± 0.014 
3.163 ± O.0S6 
2.820 ± 0.071 



Coefficient of 

Variability, 

Per Cent 



14-53 ± 0.39 

S.06 ±0.22 

24.82 ± 0.68 

14.03 ± 0.39 



From this we see that each separate character takes its own 
type and variability. For example, corn is much more variable 
as to weight (24.82 per cent) than as to any other character 
measured. This is to be expected, because weight is to some 
extent the resultant of both length and circumference and would 
thus partake of the variability of both. But we note also that 
this corn at least was much more variable as to length than as to 
circumference (14.53 per cent as compared with 8.06 per cent). 

Again we note that these ears are much more variable as to 
number of rows than as to circumference, by which we infer 
that the width of the kernels is far from uniform, else the two 
would move together. 

This raises the whole question of the relation or bond between 
different characters, a subject to be discussed in the succeeding 
chapter on " Correlation." It is sufficient here to remark that 
the typical ear of this crop of corn is 8.829 inches long, 7-047 
inches in circumference, has 20.09 rows of kernels, and weighs 
12.75 ounces. If we should pick such an ear it could stand as 



TYPE AND VARIABILITY 445 

the actual type of this crop, though the different characters 
involved would vary differently from this type or mean. 

SECTION VI — EFFECT OF SELECTION UPON TYPE 
AND VARIABILITY 

The whole purpose of selection is to influence type. In the 
minds of some it is also to reduce variability. The real effect of 
selection is well brought out in data (see table, page 446) from 
Dr. Hopkins's experiments ^ in endeavoring to influence chemical 
composition of corn by the method of selection. It is to be 
noted that all four strains sprung from the same original stock 
(163 ears), and that each seed selection was made from the 
highest (or lowest) ears within the several strains ; that is, the 
high-oil stock, for example, originated from those ears show- 
ing the highest oil content in the original stock, and was 
developed by successive selection of the highest oil ears, always 
within the high-oil stock, and similarly for the other strains. 

Discussion of data. A critical study of the columns of means 
shows a steady rise in the means of both high-protein and high- 
oil strains and a corresponding decline in low-protein and 
low-oil strains, indicating a prompt response to selection. An 
inspection of the columns of standard deviations and coefificients 
of variability, however, reveals the fact that the variability 
is practically unchanged. This agrees with the mathematical 
theory, to be developed later, namely, that the effect of selection 
is to shift the type but not greatly to reduce variability. 

The peculiarity of this sort of selection is that it is progres- 
sive ; that is to say, with each response to selection a neiv 
standard is set up still more difficult to meet than was the 
old one. Under these conditions of continuously advancing 
standards and with rapidly advancing types, in only two out of 
the four cases was the variability apparently reduced, and this 
whether we regard the standard deviation or the coefficient of 
variability. This power of response to the demands of an ad- 
vancing standard of selection is immensely suggestive and will 
be considered further under " Heredity." 

1 See Bulletin A^o. iiQ, University of Illinois Agricultural Experiment Station. 



446 



TRANSMISSION 







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TYPE AND VARIABILITY 



447 



SECTION VII — INDIRECT EFFECTS OF SELECTION UPON 
TYPE AND VARIABILITY 

In the table just given we noted only the direct effects upon 
the character undergoing selection. It now remains to consider 
how rigid selection of one character may affect other and pre- 
sumably correlated characters. To this end we construct a 
table showing the physical characters of the four strains of 
corn now under discussion, remembering that these strains all 
developed from the same original stock and that selection was 
confined to the chemical characters, protein and oil, leaving the 
physical and physiological characters free to take care of 
themselves. 

Indirect Effects of Selection : Results of Seven Ye.ars' Selec- 
'TioN for Chemical Composition upon Physical Characters. 
All Four Strains developed from the Same Original Stock ^ 





Length of Eak 


CiRCUMFEKENCE 


Variety 


I 
Mean 


2 

Stand. Dev. 


3 

Coef. Var. 


4 

Mean 


5 
Stand. Dev. 


6 
Coef. Var. 


A. High-protein . . 

B. Low-protein . . 

C. High-oil .... 

D. Low-oil 


7.21 ± 0.04 
7. So d= 0.04 
6.87 ± 0.04 
7.48*0.04 


CJ 4- vj 

If If If If 


b b b b 


17.6 ± 0.4 

19.7 ±0.4 
20.2 ± 0.4 
17.4*0.4 


5.76 ± 0.01 
6.51 ± 0.02 

6.05 ± C.OI 

6.65 ±0.02 


0.44 ± 0.01 
0.61 ± 0.01 
0.53 ±0.01 
0.59 ± 0.01 


7.6 ±0.2 
9.4 ±0.2 

8.8 ±0.2 

8.9 ± 0.2 





Number of Rows 


Weight of Ears 


Variety 


7 
Mean 


8 
Stand. Dev. 


9 

Coef. Var. 


10 

Mean 


II 
Stand. Dev. 


12 

Coef. Var. 


A. High-protein . . 

B. Low-protein . . 

C. High-oil .... 

D. Low-oil 


13.72 ±0.03 
14.17 ± 0.06 
15.65 ± 0.06 
12.80 ± 0.05 


1.85 ±0.02 
1.94 ± 0.04 
2.08 ± 0.04 
1.77 ±0.04 


13.5 =fc 0.2 
i3-7±o.3 
13-3 ±0.3 
i3-8±o.3 


7.53*0.04 

9.66 ± O.IO 

7.79*0.07 
g.84 ± 0.08 


2.50*0.03 
3.30*0.07 
2.43*0.05 
2.87 * 0.06 


33.2*0.4 
34.2*0.7 
31.2 ±0.6 
29.2*0.7 



Discussion of data. A critical study of this table reveals 
some significant facts concerning the indirect effects of selection 

^ See Bulletin Xo. iig, University of Illinois Agricultural E.xperiment Station. 



448 TRANSMISSION 

upon characters other than those under special consideration. 
Such a critical study develops the fact that these four strains 
differing in protein and in oil content have developed also into 
four distinct strains regarding the purely physical characters, — 
length, circumference, etc. 

1. HigJi and lozu protein. The ear of the former is the 
shorter (column i), and the smaller standard deviation and co- 
efficient of variability show it to be less variable as to length 
(columns 2 and 3). It is also smaller in circumference (col- 
umn 4), with a less number of rows (column 7), and lighter in 
weight (column 10). It is also less variable in every respect, 
both relatively (columns 2, 5, 8, and 11) and absolutely (col- 
umns 3, 6, 9, and 12). 

2. HigJi a7ui low oil. In the same manner we learn that the 
high-oil ear is a shorter and a smaller ear than the low-oil, but 
that it is more variable as to length and less variable as to 
circumference (columns i to 6). The low-oil ear is rapidly becom- 
ing a twelve-rowed variety, with a lower deviation than any 
other (column 8). It is the heaviest, though not the longest, of 
the four selected strains. 

3. The fonr selected strains. Of these four strains developed 
from the same original stock, the low-protein ear is the longest 
and the high-oil the shortest. The high-oil is also the most 
variable as to length (column 3). 

The low-oil is the largest and the high-protein is the smallest 
in circumference. The latter is also the least variable and the 
low-protein is the most variable as to circumference. 

The high-oil corn has the largest number of rows, with the 
lowest variability, and the low-oil the fewest rows, with the 
least standard deviation but the greatest coefficient of variability. 

The low-oil is the heaviest and the high-protein the lightest 
ear, but the low-protein is the most variable as to weight. 

It ivill be noted that these differences are the natural res? tits of 
selecting, not for these particular characters, but for chemical 
content. They are therefore the indirect effects of selection, 
and bring up again the whole subject of correlation, which will 
be treated further in a later chapter. 



TYPE AND VARIABILITY 449 



SECTION Vni — STUDIES IN TYPE AND VARIABILITY 

OF THE SAME VARIETY OF CORN RAISED UNDER 

DIFFERENT CONDITIONS AS TO FERTILITY 

The effect of the conditions of Hfe upon variabiHty, as distinct 
from mere development of the mass, is well illustrated in the 
behavior of a single variety of corn (Learning) grown under 
different conditions as to fertility. This was the crop of 1906 
upon land that had been in pasture for eighteen years previous 
to 1895, in a three-year rotation of corn, oats, and clover from 
that time till the present, with the fertility treatment indicated 
in the tables (pages 450 and 451) since the year 1901. 

Discussion of data. As to weight of ear, it will be noted (see 
tables, pages 450 and 451) that the mode and mean correspond 
very closely to yield ; that is, that increased yield is mainly due 
to heavier ears. This is inevitable from the uniform method of 
planting with two stalks to the hill. In respect to variability, 
however, we can detect little difference except in the last plot,, 
which was planted with three stalks to the hill. 

In respect to length and circumference of ear it is noticeable 
that the higher yields are accompanied by the longer and larger 
ears for the reasons given above. The most significant fact in 
the table is that corn is far more variable as to length than 
as to circumference, but that neither is especially affected by 
fertility. 

A general correspondence between circumference and number 
of rows is evident, showing a tendency to constancy as to size 
of kernel, but again variability is not greatly different for the 
different yields. So far as this instance can be accepted as a 
safe criterion, we may deduce the following principles : 

1. That type is directly and largely dependent upon food 
supply. 

2. That variability is not greatly influenced by specially 
favorable conditions of life, tending to become less rather than 
greater as all individuals are afforded ideal opportunities for 
development. 



450 



TRANSMISSION 



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452 TRANSMISSION 

Special Exercises 

The student should have extensive practice in making frequency distri- 
butions of different species and in working out standard deviations and 
coefficients of variability. He will thus not only become familiar with the 
methods of work, but he will acquire new conceptions of the whole subject 
of variability and type. The teacher should require the student at this 
point to make original studies on his own account, and to prosecute the 
work until he becomes entirely familiar both with the methods and with the 
conceptions involved. 

ADDITIONAL REFERENCES 

The Grammar of Science. By Karl Pearson. Chapter X. 
Variation in Animals and Plants. By H. M. Vernon. Chapter I. 



CHAPTER XIII 

CORRELATION 

When studying variability in its simplest form we take the 
characters separately and determine how each behaves with 
reference to itself alone ; that is, with reference to its own 
range and type. 

SECTION I — MEANING OF CORRELATION 

As the study proceeds, however, and is extended to other 
particulars, it will be noted that certain characters tend to rise 
and fall together, as if connected by some causative relation, — 
for example, length and weight of ears, or size and strength of 
horses ; while others appear to vary quite independently of one 
another, as stature and intellectual power in man, or color and 
feeding quality in animals. 

The whole subject of correlation refers to that interrelation 
between separate characters by which they tend, in some degree 
at least, to move together. This relation is expressed in the 
form of a ratio. Thus, if an increase of one character is always 
followed by a corresponding and proportional increase in a re- 
lated character, the correlation is said to be perfect and the 
ratio is i. On the other hand, if an increase in one character 
is followed by a corresponding and proportional decrease in a 
related character, the correlation is said to be negative and the 
ratio is — I, or perfect negative correlation. Still again, if the 
characters in question are absolutely indifferent the one to 
the other, the correlation is said to be zero, indicating mere 
association under the law of independent probability, without 
causative relation of any kind. 

Examples of perfect correlation are furnished by such obvious 
relations as those between the power of sight and the presence 
of eyes ; the giving of milk and the presence of an udder ; the 

453 



454 TRANSMISSION 

presence of sunlight and the fixing of carbon ; and by such 
other relations as are involved in direct causation. 

On the other hand, such a relation as deafness among teleg- 
raphers or blindness among civil engineers or locomotive drivers 
is unknown, because the conditions are such that the characters 
in question are mutually exclusive. 

In general, however, correlation falls somewhere between — i 
and unity, and on one side or the other of the zero point ; that is, 
a degree of relationship exists which is neither absolute, denot- 
ing direct causation, nor negative, signifying mutual exclusion. 
For example, a high degree of correlation exists between length 
of cob and weight of ear. It does not amount to unity, however, 
for the circumference also contributes to weight. 

Most results in living organisms are the effect of mixed 
causes, and for this reason correlations are more complicated 
than may at first appear. For example, many, if not most, good 
cows have a capacious " barrel " and a roomy udder, and men 
have been led to assume a perfect correlation between these 
special characters and milk production ; whereas the truth is 
that the correlation, though high, is something less than unity, 
because good cows are known with small barrels and with incon- 
spicuous udders. Here is a real need for accurate methods of 
determining what degree of correlation actually exists. The 
average man asks whether or not two characters are correlated, 
and expects a positive answer Yes or No ; whereas the question 
should be. To what extent do the two characters appear together.? 
expecting for an answer a fraction lying somewhere between 
zero and unity, say perhaps 40 to 60 per cent, as in correlation 
of length to weight of ear. 

The student must distinguish clearly between correlation and 
mere association. For example, we might ask the question whether 
black pigs are more subject to cholera than are pigs of other 
colors. The first step would be to establish a ratio between the 
number of diseased pigs and pigs in general. This ratio would 
now express the chances that a particular pig, irrespective of 
color, will be afflicted with this disease, — that is, by that opera- 
tion of independent probability which we call chance. If now 
we find upon inquiry that under the same conditions the ratio 



CORRKLATION 455 

of cholera subjects to black pigs is higher than the ratio to pigs 
in general, then we should conclude that an actual positive corre- 
lation exists between the black color and this particular disease. 
On the other hand, if this ratio should be below the ratio of 
pigs in general, then we should conclude that black pigs are 
less susceptible to this disease than are pigs of other colors, and 
that a negative correlation exists, assuming always equal oppor- 
tunities for infection. This is the only correct method of study, 
and it would not be safe to conclude that black pigs are pecul- 
iarly susceptible simply because most of the pigs that died under 
our observation happened to be black, for black pigs are more 
numerous in the cholera belt than all others combined, and 
under probability alone their absolute mortality must be higher. 
When expressed in the form of a ratio, however, the truth comes 
to the surface.^ 

Similarly we may ask the question whether different species 
of plants or animals tend to attract or repel each other when 
thrown together in the same territory. Here again the first 
step is to find the. ratio of association under free operation of 
independent probability, — a ratio based on the relative numbers 
of individuals of the species in question and the extent of terri- 
tory, first where no opportunity for association is possible, and 
second, where such association is possible. If the two ratios 
differ, then we infer that some degree of correlation exists. 

SECTION 11 — CALCULATION OF COEFFICIENTS OF 
CORRELATION 

When the presence or absence of the characters in question 
is absolute, as red or black hair, presence or absence of horns, 
then the correlation is expressed by a single ratio, as we have 
seen. But most cases are not of this extreme simplicity ; for 
example, it is said that white cats are deaf. If now all white 
cats are deaf, then the correlation between albinism and loss of 
hearing power is absolute, and is expressed by the coefficient i. 

1 Perhaps it ought to be remarked that this illustration is taken purely at 
random, as no studies have been made as to the relation between color and this 
particular disease. 



456 



TRANSMISSION 



Suppose, however, that out of lOOO cats taken at random 
20 are white, 10 are deaf, and 6 are both white and deaf. 
Is there correlation ? Now, according to this assumption, the 
probabiHty of a cat being deaf without respect to color is 
10-^1000, or I to 100; but the probability of a white cat 
being also deaf amounts to 5 ^ 20, or |, showing a high corre- 
lation between albinism and deafness. 

But to derive an exact expression for this correlation is not 
so simple as it might seem. According to the conditions which 
we have already laid down, and in consistency with other phases 
of the problem of correlation in general, any expression which 
we may adopt as an efficient measure of this correlation should 
be such a formula as will become zero when the two characters 
are indifferent to each other ; will become i when the two move 
together perfectly ; and will become — i when they are mutually 
exclusive. 

Yule ^ has given an elegant measure of this association, or 
correlation, which satisfies these 
conditions. To develop this for- 
mula he arranges the population 
as in the accompanying diagram 
with respect to the characters 
in question (deafness and color). 

Then the measure of associ- 
ation between deafness and the white color is expressed by 

(6 X 976) -(4 X 14) _ 
(6 X 976) + (4 X 14) 
In general, if we have a popu- 
lation arranged with reference to 
the presence or absence of two 
characters, M and N, in num- 
bers a^ b, c, d, the arrangement 
would stand the same as above, 

ad — be 





Cats 


White 


Not White 


Deaf 


6 


4 


Not deaf 


14 


976 





0.9I+. 





M Present 


M Absent 


N Present 


a 


b 


N Absent 


c 


d 



and the formula would be 



If care be taken to arrange 



ad -f be 
the table so that be shall be numerically less than ad, then the 



1 Philosophical Transactions of the Royal Society, CXIV, 257-319. 



CORRELATION 



457 



correlation is positive. Whenever ad and be become equal 

the formula becomes — -~ = o, or no correlation ; whenever 

ad + DC 

b ox c becomes zero, then the formula becomes — = i, or 

ad 

perfect positive correlation ; and whenever a or d becomes 

— be 

zero, then the formula becomes • = — i, or perfect negative 

, . be 

correlation. 

This is the simplest formula proposed that will meet the 
necessary conditions of the case. Pearson ^ has proposed several 
others that are much more complicated, and that differ slightly 
as to results. Strange as it may seem, the problem is a com- 
paratively new one, though the question involved is fundamental 
and very old. Though other methods are in use for special 
cases we may safely use Yule's formula for all ordinary cases 
of association where the question is simply as to presence or 
absence, without involving considerations of degree ; that is to 
say, when the question is whether or not the cats are deaf, 
without reference to degrees of deafness ; whether or not the 
patient has smallpox, without reference to the severity of the 
attack. 

When, however, the question is one of possible correlation 
between characters present in varying degrees^ as size, weight, 
amount of milk, etc., the problem would seem at first thought 
to be far more difficult ; but in truth it has been much more com- 
pletely worked out than the preceding question. 

For example, what is the correlation between length and cir- 
cumference in ears of corn t In general, long ears are also large 
ears, but many can be found that are long and slender, many 
that are short and small, and still others that are short and large. 
In other words, the two characters, length and circumference, 
are so related that the two maxima may appear together, the 
two minima together, the maximum length and the minimum 
circumference and vice versa, and all grades between. What 
now is the correlation .'' To answer a question thus complicated 
we construct what is called a correlation table. 

^ Philosophical Transactions of the Royal Society^ CXCV, 1-47. 



458 



TRANSMISSION 



SECTION III— THE CORRELATION TABLE 

To determine the degree of correlation between any two 
characters in any race, a so-called "correlation table" is con- 
structed out of the measurements of the two characters as found 
in a large number of individuals, one character being recorded 
in columns and the other in rows. Two records are thus made 
of the same individual, one for each character. Such a table, 
when finished, consists of a double system of arrays, each 
dependent on the other, and from whose means and standard 
deviations the mutual relationships can readily be worked out. 

Knowing this relationship and the value of one of the char- 
acters we are enabled to calculate the corresponding mean value 
of the other. The advantages of this for purposes of selection are 
obvious. The method is best illustrated by an actual example. 

For instance, it is evident that the weight of ears in corn de- 
pends partly upon their length and partly upon their circumfer- 
ence. To what extent, for example, does it depend upon length ? 

In order to answer this question definitely a large number of 
ears taken at random are both weighed and measured, and the 
data are arranged in tabular form as described above, appearing 
as follows : 

Correlation between Weight and Length of Ear 
(Leaming Corn) 

Weight of Ears in Ounces 



I 
I 
I 

4 
7 
15 14 



8 4 



6 II 26 II 

iS 



2 12 16 13 13 6 I 



20 12 
7 19 



6 
12 12 
13 



II 4 
21 II 

5 17 22 



3 1 • 
9 23 30 26 26 5 I 
7 10 23 35 26 24 12 
I 4 14 19 29 17 10 
I I 3 8 18 10 6 
■ • • 2367 



CORRELATION 



459 



Arrays of a correlation table. In this table each ear is 
recorded in the proper square to represent both its weight and 
its length. This being the case, all the ears of the same weight 
that are also of the same length are recorded together in the 
same square. This means that the various rows are frequency 
distributions of weight tvith respect to length (as i, 6, ii, 26, 
II, 8, 6, I, the frequency distribution corresponding to the 
length 6.5 inches), and all the coIhudis are frequency distributions 
of length with respect to weight. Such frequency distributions 
with respect to a cori'clated character are technically known as 
"arrays." The entire table, therefore, may be looked upon as 
made up of two systems of parallel arrays with respect to the 
two characters in question. They are in no respect different from 
any other freqtiency distributions ; and their means, standard 
deviations, variability, and other determijiatio7is are calculated 
by the same methods as given in the last chapter. 

SECTION IV — THE CORRELATION COEFFICIENT 

A mere inspection of the correlation table just given suggests 
that, in general, short ears are light ears, and that long ears are 
heavy ears ; but what we seek is a statistical constant which 
will be a measure of this correlation, and which indicates to 
what extent the weight of ears can be predicted from their 
lengths. The coefficient of correlation is such a constant, and 
when determined it will be denoted by r. 

A discussion of the mathematical theory of correlation will 
be given in the Appendix, but it should be said here, as before, 
that the coefficient always takes some value between + i and 
— I. If r = + I there is said to be perfect positive correla- 
tion ; that is, the two characters are causally connected. If 
r = — I there is perfect negative correlation; that is, they 
are mutually exclusive. If no correlation exists, r=0, indicat- 
ing the two characters as being indifferent to each other and 
moving independently. In nearly all cases some actual correla- 
tion exists, and, in a general way, we may say that the correla- 
tion should be judged by the value which r takes between zero 
and unity. 



460 



TRANSMISSION 



Method of finding correlation coefficient. The method of cal- 
culathig the correlation coefficient (r) is exhibited in connection 
with the table on page 461, showing a representative case, for 
convenience continuing the same correlation table already con- 
structed. Though the method is somewhat complicated it is 
given in full. 

It is highly important to get at once a general conception of 
this table and of the method of procedure. All the computa- 
tions shown except those involved in the column headed %P 
have to do only ivith finding the means and standard deviations 
of the population with respect to the two characters in question, 
according to the method fully treated in the last chapter ; that 
is to say, the columns of figures headed ^ f,, /z.^/-> ^i^ ^l^ 
Il^l^ fin fir^^in ^/r» D „}, fj,.D ,^?' are all self-explanatory to 
^ny one familiar with the meaning of ordinary algebraic symbols, 
and who knows how to find the variability of a population by the 
methods already given. 

There remains the column of figures headed %P, which it 
seems worth while to explain in detail and which is the only 
special feature in the determination of the correlation coefficient. 
Each number in this column represents the sum of the products 
of the corresponding length and weight deviations for every 
individual in the horizontal array to which the number belongs. 

To show how these numbers are computed, select, for example, 
the horizontal array marked 10, and we shall show how to find 
the number 431.0. 

In this case 

10 — 7.8, the mean, = 2.2 = Dj of row 10. 
Then 

2.2 [i (- 0.7) + I (0.3) -I- 3 (1.3) + 8 (2.3) + 18 (3.3) 

+ 10 (4.3) + 6 (5.3) + 4 (6.3) + 2 (7.3)] = 431.0. 

All other numbers of the column headed ^/'are found in the 
same way, and the total is written symbolically as 'S,D^D,^.? 

1 Read "/sub //-," meaning the frequency of weights ; "/sub ;/■ T'sub //•," mean- 
ing the frequency of weights multipUedby the value in weights ; "/sub /.," mean- 
ing the frequency of length, etc. 

■^ The real significance of S/" is best shown by the expression SZ?/,Z>//-, that 
is, the sum of the products of both deviations of all the individuals in the table. 
It is written in various ways, but always with the above meaning. 



CORRELATION 



461 



Correlation of Weight of Ears relative to Length of Ears 
(Leaming Corn) ^ 

IN Ounces 



Weight of Ears 

O " M 



\0 r^ 00 CT* 



A fJ\ D^ Dl f^Dl SP 



3- ' 

3-5 ■ 

4- 3 
4-5 • 

5- • 
5-5 • 
6. . 
6.5 . 
7- • 
7-5 • 



8.5 

9- 

9-5 



724 

15 14 8 4 I 

12 16 13 13 6 I 

6 II 26 II 8 6 I 

2 2 12 iS 12 12 II 4 I 

I 2 4 20 12 13 21 1 1 6 6 I I . . 

• • 3 7 19 25 17 22 17 3 I •• • 

I I 12 9 23 30 26 26 5 I . . 

. . . . I 7 10 25 35 26 24 12 12 

I 4 14 "9 29 17 10 ' 3 

I I 3 8 18 10 6 4 2 

23672s 



142 
100 
53 
26 



12.0 


-4 


8 


23 





92. 


■7-5 


-4 


3 


18 


5 


92. 


56.0 


-3 


8 


•4 


4 


201. 


72.0 


-3 


3 


10 


9 


174. 


95 -o 


— 2 


8 


7 


8 


148. 


291.5 


— 2 


3 


5 


3 


280. 


3«4.o 


-I 


8 


3 


2 


204. 


455-0 


-I 


3 


I 


7 


119. 


525.0 


- 


8 





6 


45- 


735-0 


-0 


3 





I 


9- 


912.0 





2 








0. 


II39-0 





7 





5 


67 


1278.0 


I 


2 


I 


4 


.98 


950.0 


I 


7 


2 


9 


290 


530.0 


2 


2 


4 


8 


254 


2730 


2 


7 


7 


3 


.89 


55-0 


3 


2 


10 


2 


5' 


"•5 


3 


7 


13 


7 


13 



1430 
156.9 

394-4 
347-2 
297.6 
618.9 
465.8 
306.8 
no. 8 
8 14.9 
1.4 
129.6 
466.3 
564.4 



431 



8 364.0 
o 107.2 
7 27.0 



"^ 



>, CO vO 00 



-*■ o o - 



■^ \0 ^O t^ o^ 



I I I I I I 



00 00 cr 





> O O M 

Notation: 



o t-^ t^ 



2 + 



II. 5 2432.9 4947-2 

^A= 7-85- ±0.03 

(7 £^=2.45 

<''l= 1.57 ±0.02 

4947-2 
r = = 0.87 

993(i-57)(3-63) 

j,^ ^ 0.6745 (i-r2) ^ „ 

correlation coefficient 
= o. 87 ± 0.005 

, — vL = 2.03 ± 0.02 

= regression of weight 
relative to length 
r = 0.3a ± 0.005 



= regression of length 
relative to weight 
f\^= class frequencies of total population with respect to length. 
?'l= value or measurement corresponding to a given frequency with respect to length. 
M ^=^ mean length of ears. 

D^=, deviation of ear lengths from mean length. 
<T\^= standard deviation of length of ears. 

f^f|— class frequencies of total population with respect to weight. 
V^ = value corresponding to a given frequency with respect to weight. 
M^ = mean weight of ears. 
■Ovv= deviation of weight from mean weight. 
0'l= standard deviation of weight of ears. 
r= coefficient of correlation. 

r -A- = coefficient of regression of weight with respect to length. 
' We have retained a minimum of decimal places in this table in order to save space. 



462 TRANSMISSION 

The value of r is found by means of the formula 
r = 

Systematic arrangement of work. The whole process, which 
seems somewhat complicated, is after all quite simple. To 
recapitulate, it amounts to multiplying the figures in each square 
by both their own deviations (that is, by their deviation as to 
length and their deviation as to weight), and then adding all the 
results and dividing by the whole number (of ears) multiplied 
by the product of the two standard deviations. (See formula 

r~ — -•) In performing the actual work, however, it is 

highly important to have a systematic scheme for carrying out 
the computations in order to avoid confusion in the somewhat 
comphcated details. It has seemed desirable, therefore, to 
present the matter in the form of a detailed description of the 
various steps involved. 

First step. Having given the correlation table of the popula- 
tion, we first add the frequencies in the arrays with respect to 
both characters ; that is, add the numbers in columns and rows 
of the table. This gives two frequency distributions of the total 
population, — the one with respect to length of ears (/^), and the 
other with respect to weight of ears (/„). 

The one with respect to length has the frequencies 4, 5, 14, 
16, 19, 53, 64, 70, 75, 98, I 14, 134, 142, 100, 53, 26, 5, I. 

The one with respect to weight has the frequencies 4, 22, 27, 
50, 47, 71, 75, 71, 75, 88, 107, 114, 112, 65, 37, 8, 13, 4, 2, I. 

Second step. F"or each of these frequency distributions 
(column f I and row /„.) the means and the standard deviations 
must be calculated. The method of making these calculations 
is the same as the one used for mean and standard deviations 
in general. It has already been fully explained, and therefore 
need not be repeated here. A systematic arrangement of the 
work is shown in connection with the table. The results are : 

mean length = Mi = 7.85 
standard deviation in length = o-/ = 1.57 

mean weight = M„- = 10.65 
standard deviation in weight = o-,,. = 3.63. 



CORRELATION 463 

Third step. This is the only part of the work that is really 
new. In doing the second step we found the deviations of 
the classes from the mean length and mean weight. These are 
recorded under Z>^ and Z>,^.. For example, in row i we find 
that 4 ears were each 3 inches long ; that is to say, they 
deviated — 4.8 inches from the mean length taken at 7.8 in- 
stead of 7.85 in order to save labor. We next take the num- 
ber in each square of the correlation table and multiply it by 
the corresponding deviations both in weight and in length, 
thereby securing a product which is the result of the full num- 
ber of variates involved and of their deviation in respect to 
both characters. 

For example, where the column headed 9 ounces and the 
row labeled 6.5 inches cross each other occurs the number 
8, which indicates that 8 ears of the population weighed 9 
ounces and were 6.5 inches long. In other words, these 8 
ears each deviate — 1.7 ounces {row D,,, column 9) from mean 
weight of ears, and — 1.3 inches from the mean length (column 
D^, row 6.5). Hence for this number 8 we form the product 
8(— i.7)(— 1.3) = + 17.68. Without regard to labor, we should 
find such a product for each niiinber in the eorrehitioi table. 
If now all these products be added and the result divided by 
the product of the two standard deviations into the number of 
variates in the total population, we shall obtain the correlation 
coefficient, or the index of correlation which we seek. 

The systematic way of carrying out this work is to record the 
results of this operation for each horizontal array under the 
heading 2/*, and then add these results for the arrays to obtain 
the final result 4947.2, which is symboUcally indicated by 
2Z>/Z>/,-, or summation DjD,,-. 

To illustrate the method of calculation a few of the products 
recorded in column S/'will be shown. 

For example, with 7.8 as the mean length and 10.7 as the 
mean weight, we have for the array corresponding to length 

4 inches, 

-8.7 X 3 ^ 

- 3.8 X - 6.7 X 5 [ This gives 394.4. 

- 5.7 X I 



464 TRANSMISSION 



For the array corresponding to 5 inches, 

[ This gives 297.6. 



- 7.7 X 2 
-6.7 X 4 

X- 5.7 X 7 

- 4.7 X 2 

- 3-7 X 4 



Treat all arrays in a similar manner, and, finally, divide the 

sum of all the products thus obtained (that is 4947.2) by the 

product of the two standard deviations and the number of 

variates, being careful ahvays to preserve tlie full distinction as 

to plus and minus signs. This gives 

4947.2 

r = ; -— — --- = 0.87, the correlation coefficient. 

993(1-57) (3-63) 

The mathematical derivation of this coefficient as a measure 
of correlation involves too much mathematics to be given here. 
It may be noticed from the common-sense standpoint, however, 
that it seems to be a good measure of correlation. To appre- 
ciate the meaning of this coefficient, it should be recalled that 
we take the products of both deviations for every individual in 
the table, add these products, and divide the result by the 
number of individuals. This gives the average of all the 
products of both deviations. We then divide this average 
product of the individual deviations by the product of the two 
standard deviations, thus securing an expression whose value is 
influenced by the deviation of both characters with reference 
each to the other. 

It requires but little mathematical insight to see that if the 
correlation is positive and considerable, positive values of the 
two characters correspond and negative values correspond ; and 
further, that all the products of deviations are positive. This 
makes for a large correlation coefficient. On the other hand, if 
no correlation exists, for any value of one character we may 
expect in the long run equal and opposite deviations of the 
other character, which makes the sum of products of deviations 
very small. This common-sense examination indicates the real 
nature of the correlation coefficient. 

Fourth step. Find the probable errors in the determined values. 
Those in the means and standard deviations are computed by 



CORRELATION 465 

formulas stated in the last chapter. For the probable error m 
the correlation coefficient use the formula 

^0.6745(1 -r-) , ^ [i-(o.87)2], 

£r = ± ^^ \- = ± 0.6745 ^,,:r::^-^-J ± O.OO5. 

V// V993 

Use of correlation coeflScient. The correlation coefficient is a 
good index of the mutual relation that exists between the char- 
acters in question. If it is low, it indicates that they do not 
depend very much upon each other; if it is high, it indicates 
that they are in some way closely related ; and if it rises to 
unity, this relation amounts to causation, — that is, one is the 
cause of the other, or else they are the joint effect of the same 
causes. The practical advantage of this knowledge for purposes of 
selection is obvious, especially when one character is easily seen 
and readily examined and the other is not. An application of the 
correlation table would correct many popular delusions on this 
subject, as, for example, the selection of cows by the escutcheon. 

Shorter method for calculating r, the coefficient of correlation. 
There is derived in the Appendix a formula which gives 

the same numerical value for r as — - already used ; and 

while its algebraic expression is a little more complicated, it is 
much better adapted to numerical calculation, as it avoids the 
use of decimals until almost the end of the work. In this respect 
it is similar to the shorter method presented for calculating the 
standard deviation. If applied to the case of the length and 
weight of ears of corn the formula is 

r = = 6/ 6/ 

where Dj', D,,'- are deviations from our guess at the means instead 
of deviations from the mean itself as D^ and D,,-\ and Cj and C,,- 
are the corrections applied to the guesses at the mean length 
and weight respectively as used in the shorter method of finding 
standard deviation. 

In other words, we find the standard deviation by the shorter 
method explained on page 429. Then, in forming the sum of 
products of deviations, we measure the deviations from the 
guess instead of measuring them from the means, and divide as 



466 TRANSMISSION 

before by the product of the number of variates and the two 
standard deviations. Finally we subtract from this result the 
products of the two corrections to our guesses in finding means, 
after dividing that product by the product of the standard devi- 
ations of the two systems of variates. 

We shall present on page 467 an illustration of this shorter 
method, using for the purpose the correlation between length 
and circumference of ears of Leaming corn. In this G, and Gc 
are the guesses at the class mark nearest to the mean of the 
population as to length and circumference respectively. 

Let M, and M^- be the mean length and circumference respec- 
tively, and Ci and C^ the corrections to Gj^ and G^. which give 
J/^ and J/,., so that J/^ = (?^ + Q and M^ = Gc-^ Cc- 

Also let D' and Dc represent deviations of class marks 
from the guesses G, and G^ respectively. 

Unless one carries through a large number of decimal places 
the method previously discussed is not only very laborious but 
it is much less accurate than the shorter method here described. 



SECTION V — THE REGRESSION COEFFICIENT 

From the correlation coefficient and the standard deviations 
with respect to two characters it is easy to obtain what is known 
as the regression coefficient. To obtain the regression coefficient 
of the weight of ears relative to their lengths, multiply the 
coefficient of correlation by the standard deviation of weight, 
and divide the product by the standard deviation of length. 

This gives, for the regression of weight relative to length, 

r — = 2.03. 
Similarly, the regression of length relative to weight is 



Use of the regression coefScient. The regression coefficient is 
useful for prediction ; that is to say, if we know the deviation 
of one character from its mean, this coefficient will enable us to 



CORRELATION 



467 



Correlation Study (Leaming Corn Crop, 1905) 



(^ 6 

, 7 

== 7 

^ 8 



II. 5 



Circumference. Gc=6.3 



5.1 5.4 5.7 6.0 6.3 6.6 6.9 7 



23 26 

21 17 

10 iS 

9 6 

I 5 



19 7 

23 12 

22 21 

27 25 

42 33 

32 iS 

15 12 

6 II 



4 A ^l' A-D^' {D^y- f{D^Y 



4 


-5 


6 


-4 


14 


-4 


16 


-3 


'9 


-3 


53 


— 2 


64 


— 2 


70 


-I 


75 


— I 



•34 

142 
100 
54 
26 

5 



-27 

-56 
-56 

-57 
-32 
-128 
-105 
-75 
-49 



995 )-'55-o 
Cl= -0.156 



20.25 


121 


50 


16.00 


224 


00 


12.25 


196 


00 


9.00 


171 


00 


6.25 


33" 


25 


4.00 


256 


00 


2.25 


157 


50 


1. 00 


75 


00 


0.25 


24 


50 


0.00 





00 


0.25 


33 


50 


I. CO 


142 


00 


2.25 


225 


00 


4.00 


216 


00 


6.25 


162 


50 


9.00 


45 


00 


12.25 


12 


25 


995)2493 


00 




2 


506 






2 


024 

482 


O-L 


= I 


575 






3 m N * N 


O'coOCO N -^roO^ 





1 1 1 1 1 


- - - -1- N 



II 



Q 
^ 



2 fS 



■* t^ sO 



Mc 



■ 7-844 

: 6.570 



468 TRANSMISSION 

predict what will probably be the deviation of the correlated char- 
acter from its mean. Thus, suppose we select ears which deviate, 
say two inches, from the mean length of ears ; that is, which are 
two inches above the average : the regression coefficient (2.03) 
of weight relative to lengtJi indicates that ive should expect such 
ears to be abotit 4.06 ounces from the mean, that is 2 X 2.03. 
To be more general, if we select ears which have any deviation 
X from the mean length, we should expect their deviations in 
weight to center about a value 2.03 x from the mean weight of 
ears for the whole population. 

The regression coefficient is thus a fixed ratio between devia- 
tions of correlated characters, so that, knowing how much one of 
the characters differs from its mean in any unit of measurement, 
say inches, we are enabled to predict how much the associated 
character departs from its mean in its unit of measurement, say 
in pounds. Thus if a regression coefficient of weight upon stat- 
ure is, say 2.17, we know that any departure from the mean 
stature will be followed by a departure 2.17 times as great in 
respect to weight, using in both cases the same vmits as were 
used in calculating the coefficient ; for example, feet and pounds, 
inches and ounces, or even inches and pounds, if these were the 
units actually used in computing the regression coefficient. 

SECTION VI — STUDIES IN SPEED RECORDS OF 
TROTTERS 

Studies were made of 13,879 trotters possessing records of 
2 : 30 or better, in order to learn their distribution as to speed, 
and the possible correlation of speed with color, and more par- 
ticularly with sex (see tables, pages 469 and 470). 

The data were taken for each quarter second, and the record 
made a scroll over forty feet long. The matter is here con- 
densed to differences of one second in order to bring it into 
suitable space. 

The original record showed two strange peculiarities. Almost' 
invariably the largest number of records was found on the first 
quarter second after the even minute, as 20|, 21^, etc. ; that is 
to say, the records were not evenly spread, or, as mathematicians 



CORRELATION 



469 



a 

CO 
Q 
< 

o 

o 
U 

X 
H 



O 

H 
< 

O 

u 

Q 
Z 



w 

H 
H 



sivxox 


to c- 0- 
^ in cN r^ 
f X> CO 1/1 CO 

■fl- CO 00 m CO 





ir> « so « r^ 


CO 


2, 2, S 8 " 

CO CO sC N 
CO CO SO ^ M 


00 


«n ■* c CC t^ 
C 1^ SO •- 00 


vO 


« t^ 0~ -»• CO 
>- 00 0- 10 >n 
■* CO t^ -<f r) 


t 


00 t^ sO 00 -* 

N N 10 CO 00 


I 


>o -t 1- 

■* N tV - 00 


1 


N sg 00 00 

cs p^ ^ CO r>s 


" 


•* CO t-^ t^ 
so SO T 
N M CO Pi sO 


1 


iO N t^ 00 U^ 

C CO 00 I^ sD 


I 


CO "^ t^ CO 

wi CO 00 r^ s5 





C^ t". ^ i-i 

PI - CO « so 


0- 
00 


0-000 


T 


00 00 sD f) 00 
PJ 0> N ^ -O 




Cs P» « p^ O) 
C* sO sO CO -* 


b 


- 00 Cs CO pg 
t^ CO 00 Cs 


I 


1- ^ 00 t^ 10 

sO "1 -. t^ Cs 


7 


"1 t^ p) C) -^ 
-)- to 00 in ?> 


7 


li^ N IM 2, 3, 


~ 


r^ sO CO CO \0 


T 




t^ r^ 


1 


f 1 C- >t CO « .n 

00 1 - - N 


=^ j O^ f f) t^ 


f^ 1 


t 




T 


1 - - 1 - 


^ 


M M tS N ■«• 


Seconds 

Above Two 

Minutes 


a -a rt i; 
(fl 1; "= ^ 
t^; C H S 



sD 


so 


00 





sg 




c^ 


■<t 







OS 




so 


-0 


s; 



r^ 


^ 


CO 

1- 


§ 


'J- 





r 


so 

sO 


G- 


sS 


1 


sO 


t^ 


s 


sg^ 
so 


z 


00 





0- 


sO 


?? 


5^ 


sO 


so 


^ 


CO 



sO 


OS 








CO 


s; 


" 


% 


0- 


s 


00 





;? 


t^ 


sO 


sO 


p> 


sg 


CO 





" 


r^ 


sO 


s 





x 


Ss 


•" 




2 





OS 


so 


r^ 


" 


;; 


:: 


-0 


00 


I^ 


z 


- 


-i- 


2 


S 


■^ 


SO 


so 


1 


;: 


00 


s 


00 


:^ 




sO 


" 


c 


.0 


? 





c 


S 


- 





" 


C 


t^ 


s 


sD 


- 


^ 


" 


-1- 


pI 


S' 


fl 


" 





* 


sO 


:: 


:: 


t^ 


1 


- 


1 


cc 


:? 


i!? 


^ 


1 


00 


' 


sO 


'J 





: 


1 


t^ 


1 


Y? 


CO 


so 


- 


1 


CO 


- 


;; 


:: 





C' 


1 


•* 


" 


r>. P, CO to , 




2 


- 


p. 


- 


1 






CO 1 PI 1 1 




- 


- 


1 


1 


1 






- 1 1 1 1 




" 


1 


- 


- 


1 






(5 


^ 




c 



3 

c 


C 
3 


c 




c 
c 



470 



TRANSMISSION 



say, they were not " smooth," and if the curve were platted there 
would be an unaccountable "hump" at each quarter second. 

The second i)eculiarity had reference to the last record, 2 : 30. 
By the i)rincii)le just stated this number should hav^e been about 
70 per cent of the number recorded at 2 : 29^. On the contrary, 
it was very much greater. On the principle runnini;" through 
the rest of the records we should predict the number at 2 : 30 to 
be about 727, whereas the number actually recorded is 1097, 
showing conclusively that some 370 horses had been admitted 
to the 2 : 30 list that really belonged at 2 : 30 j or slower ; all of 
which shows how statistical studies bring to the surface as noth- 
ing else will the natural irregularities of observations or whatever 
abnormal facts connect themselves with our investigations. The 
table on page 469 is suggestive in many ways. 

Rei-.ation ok Skx and Color to Speed as expressed in 
Rate Per Cent 





2:30 AND Below 


2 : 15-2 : 16 AND Bki.ow 


2:10-2:11 AND Below 


Description 
















Number 


Per Cent 


Number 


Per Cent 


Number 


Per Cent 


Sex 














Stallions .... 


4.493 


32.0 


330 


36.0 


68 


39-0 


Geldings .... 


3,866 


28.0 


224 


24.0 


42 


24.0 


Total Males . . 


X-359 


60.0 


554 


60.0 


1 10 


63.0 


Mares 


5.5-0 


40.0 


36. 


390 


66 


37 -o 


Total .... 


13.879 




915 




,76 





( olor 
Bay . . . 
Black . . 
Brown . . 
Chestnut . 
Dun . . . 
Oray . . . 
Roan . . . 

Total . 



7.37C> 
1,362 
1,885 
2,220 
60 

75^ 
224 

'3.879 



53-0 

10.0 

13.0 

16.0 

0.4 

6.0 

••5 



502 
101 
129 
126 

2 

46 
13 



915 



55-0 
I i.o 
14.0 
14.0 
0.0 
5-0 
'•5 



9- 
25 
24 

-5 
o 

7 
3^ 



52.0 

14.0 

14.0 

14.0 

0.0 

4.0 

2.0 



l*"r()m the table abox'c it ajijiears that there is little relation 
between speed and either sex or color. It is true that, as we 



cx)RRi:i,.vriON 471 

road across the tabic, \vc sec ihal Ihc pcrccntai^c of Icinalcs lalls 
slii;hlly as \vc ^cl into hi,i;li speeds, but the tall is \cry sli5;lu. 
The percentai;es as It) color vary but slii;htl)', except in black, 
which decidedl)' increases with high speed, ami in gra)', which as 
deciiledly tails off. 

Applying Yule's formula to the study of these figures, let us, 
for example, take the bay color and inc|uire as to the measure 
of correlation between this co\{)v ami high speed : 

'I'olal iiuiiihcr of hays 7)37^> 

Nunihor of bays at or l)elo\v 2 : 1 5-2 : 16 502 

Total luiinhcr of performers i3i<^79 

'I'otal nunilHM- of iKMlornu'is at or l)elo\v 2 : 15-2 : 16 . . 1)15 

Nuinhcr not bays at or l)clo\v 2 : 15-2 : 16 is 915 — 502 = 413 

Niiinl)or of bays aboye z : 1 i;-2 : 16 is 7376 — 502 = 6874 

Number not l)ays al)oye 2 : 15-2 : 16 is 13,879 —(7376 + 413) = 6090 

Arranging these \alues according to \'iile's lorimila, we ha\e 



Bay 


Not Bay 


2:15-2:16 

OK UBLOW 


413 


Abovb 2:15 6874 


6090 



This gi\es as a measure of the association of the bay color 
and speed, 

6090 X 502 — 6874 X 4«3 



6o()o X 502 + 6874 X 413 



= + 0.038. 



While this resiill, 0.03S, shows that the ba) s ha\e furnished 
slightly more than their shaic of the high-speed trotters, it is 
doubtful whether this c-ocl'ticiciU is large enough to enable us to 
assert any decidcil conclalion. 

In much the same way exhaustive studies should be made in all 
lines of breeding, and at any expense of time and labor, in order 
that we may possess ourselves of reliable intormation in rcgaixl 
to as many details as possible concerning the relations of notable 
characters in our most valuable races. 



472 TRANSMISSION 

Summary. Correlation is generally a relative matter, and 
impressions are exceedingly deceptive. Nothing but actual cal- 
culation will show the extent to which characters really move 
together, and the importance of this knowledge is ample recom- 
pense for all the labor involved. As will be seen later, the same 
methods give us the only reliable measure of heredity. 

Special Exercises 

Again let the student actually do the work of finding correlation coeffi- 
cients until he acquires facility in operation and a distinct conception of 
what is involved. 

ADDITIONAL REFERENCES 

Correlation in Rye. Experiment Station Record, XIII, 241, 641. 
Correlation in the Parts of Corn. By A. A. Brigham, Gottingen. 

Experiment Station Record, VIII, 486. 
Correlation in Wheat. Experiment Station Record, IX, 553. 
Correlation Mathematics. Science, XXII, 309-312. 
Correlation of Characters in Corn. (German.) Experiment Station 

Record, XVI, 461. 
Correlation of Seeds and Color of Fruit. Experiment Station 

Record, XI, 932-936. 
Correlation of the Mental and Physical Characters in Man. 

By Alice Lee and Karl Pearson. Proceedings Royal Society, LXXI, 

1 06- 1 14. 
Correlation Theory. Science, XXI, 32-35. 



CHAPTER XIV 

HEREDITY 

" Heredity " refers to the distribution of racial characters 
among individuals of successive generations. On the principle 
of heredity all successful breeding operations depend, and the 
practical breeder needs to know all that is to be known concern- 
ing the manner in which succeeding generations are built up out 
of those characters which constitute the heritage of the race. 

To define "heredity" as the direct and personal relation 
between the individual parent and the individual offspring is 
not only to restrict its meaning within too narrow limits but to 
destroy its significance to the breeder and deceive him as to 
the actual facts of transmission during descent. "Heredity" 
properly refers to the group that constitutes the parentage and 
the related group that constitutes the offspring. 

All investigations show that both groups vary greatly among 
themselves, and to predict about where, within the racial range, 
an individual will fall as compared with its personal parent, — 
this is the object of a critical study of heredity, and the constant 
aim of the practical breeder. There is no hope that the offspring 
will be like the parent, except in a very general sense, but to 
predict how near it is likely to approach the parent, — this is 
something that requires not only the widest knowledge of the 
ancestry but the most accurate understanding possible of the facts 
and principles of heredity. It is the purpose now to inquire some- 
what specifically into some of these general facts and principles. 

SECTION I — HOW CHARACTERS BEHAVE IN 
TRANSMISSION 

The particular characters that associate themselves together, 
constituting a race, variety, or breed, have separate histories as 
the generations come and go. Each has an identity and a history 

473 



474 TRANSMISSION 

of its own, and each establishes and maintains, apparently, fairly 
definite relations to certain of its associates (correlation), while 
with reference to others it seems indifferent if not independent. 

Individuals inherit differently. All individuals of the same 
race possess the same characters, but in different proportions, 
and no two individuals, even from the same parents, are alike. 
Some portion of this difference is of course due to development 
according to the conditions of life, yet all evidence goes to show 
that, after full allowance is made for this factor, natural differ- 
ences exist that can be due only to inheritance. 

That each individual is in possession of all the characters of 
the race is evidenced by the fact that his descendants possess 
them and that he transmits far more characters than are de- 
veloped sufficiently to be noticeable in his own personality. 

Latent characters. Thus characters may be present, but 
undeveloped, or " latent." Galton asserts that latent charac- 
ters are "not very numerous";^ but it is certain that many 
characters may remain undeveloped through life and yet be 
transmitted perfectly. Familiar examples are the occasional 
secretion of milk by the male sex, already alluded to, and 
the transmission of the milking quality by bulls as well as 
by cows. All things considered, it is safe to say that the visi- 
ble and fully developed characters of an individual constitute 
but a small proportion of his real possessions. Especially may 
this be said of a highly differentiated race. 

Inheritance not limited to sex. It has been a favorite saying 
.that certain characters are transmitted to one sex but not to the 
other. There is no evidence of any such limitations to inherit- 
ance. The limitations of sex may and do prevent the develop- 
ment of many characters that we know to be potentially present, 
so far as inheritance is concerned, because they can be trans- 
mitted. In this respect the relation of the male mammal to milk 
secretion is not different from that of the female that has never 
yet borne young. The faculty is latent,^ or undeveloped, in both 

^ Gallon, Natural Inheritance, p. 187. 

2 The term " latent " is unfortunate. It conveys too strong!}- the sense of 
lurking. "Undeveloped" is the sense that ought to attach to this unfortunate 
term that has now been used too long to be dislodged. 



HEREDITY 475 

cases. They differ only in the fact that with the female the 
development is easily brought about, while in the male it is 
difTficult and in most cases impossible. ^ 

Belated inheritance. It is well known that all characters do 
not develop contemporaneously. Thus the sexual characters 
become developed just before full stature is attained, and with 
the failure of the primary sexual characters with advancing age 
comes the development of many of the peculiarities of the other 
sex. Then it is that the hen crows, the human female grows 
more hair, and the voice of the male becomes effeminate. The 
term "belated inheritance," though fixed in our literature, is 
unfortunate. It is belated development that is meant. Inheritance 
comes only at, or rather before, birth ; but development is con- 
ditioned upon many factors, — among which age and sex are 
important, but not the principal, considerations. 

Blended and exclusive inheritance. Perhaps the first and 
most noticeable fact is that some characters blend when brought 
together by transmission, while others remain distinct, being 
apparently mutually exclusive. Thus skin color in man blends 
readily, the cross between white and negro being nearly always 
of some shade intermediate between those of the parents, — 
almost never spotted. ^ In Shorthorn cattle and in Jerseys the 
colors frequently, if not generally, blend, while in the Holstein- 
Friesian they always remain distinct. In horses the blend is 
common, but in hogs it is practically unknown, so that in a 
litter of pigs from a black and a white parent the colors will 
remain distinct ; some may be black, some white, and others 
spotted, but none will be roans or grays. 

The same distinction holds as to characters generally. Some- 
times the offspring will be intermediate between the parents, 
showing a blend ; and again it will resemble one or the other, 
or else exhibit traces of both, each distinct and separate. 

For example, so far as the matter has been studied, the blend 
is most perfect as to stature,^ and probably as to size in general, 
but eye color does not readily blend ,^ nor do " tempers " ^ or 

1 The student is reminded that milk secretion among males is not unknown. 

2 The spotted skin is not absolutely unknown among humans, however. 

3 Galton, Natural Inheritance, p. 89. * Ibid. p. 145. ^ ibid. p. 233. 



476 TRANSMISSION 

" tastes." This being true, we are often disappointed in trying 
to modify or tone down a vicious disposition by mating with 
one of milder temper, the progeny tending to follow the average 
of the race, or else to be as vicious as the objectionable parent. 

Particulate inheritance, — inheritance by type, or bit by bit. 
Characters are often so closely associated (correlated) as to 
move in company, so that whole groups of characters appear 
and disappear together, even when there is little or no known 
causative relation between them. Whether this is merely acci- 
dental association of characters not mutuallyexclusive, and certain 
to happen occasionally under the law of chance, or whether it 
is due, rather, to some deeper-lying principle, is perhaps uncer- 
tain ; but it is surely true that man, for example, runs in types, 
and whoever has traveled much, or has enjoyed a fairly exten- 
sive acquaintance, has met many people of no blood relationship, 
in places widely separated, who yet were clearly of the same 
type, and whose similarity became more evident upon closer 
acquaintance.^ 

Clearly, characters are not altogether independent one of 
another, and often the greatest difficulty is encountered in 
breaking up a group, some members of which are desirable and 
others objectionable. So inheritance is often " bit by bit," as if 
the unit of transmission were larger and more complex than the 
single character ; as if a kind of permanent partnership were in 
force. The biological basis of all this, if it really exists, will 
probably remain for a long time hidden, but coefficients of 
correlation afford at least a method for determining the degree 
and the persistence of this copartnership. 

Polymorphism and sexual dimorphism. Many races, instead 
of showing all intermediate gradations from one extreme to the 
other, in respect to size for example, or color, or any other 
character or association of characters, will exhibit two, three, 
or more forms or types, so different and distinct as often to be 

1 In practical breeding operations the greatest need exists for e.xact knowledge 
of correlated characters. The methods given in the preceding chapter enable the 
student to determine quantitatively the real extent of correlation, and breeders 
should prosecute most industriously the study of this subject, until they are well 
informed as to the real relations of all valuable characters of domesticated 
animals and plants. 



HEREDITY 477 

mistaken for distinct species. In other words, their variations 
are not continuous but discontinuous. 

Thus the earwig is of two distinct types as to size (dimorphism), 
and many insects exist in three different forms, — larva, pupa, 
and imago, — the crawling or worm form, the resting stage, and 
the winged form.^ 

Sex in general means dimorphism, for, almost invariably, 
marked differences exist between males and females of all 
species. Sometimes, as in most mammals, the males are the 
larger, but often the opposite is true, as in the case of many 
birds and insects. External differences other than size, how- 
ever, are certain to distinguish the sex by a number of non-sexual 
characters. 

Dimorphism in improved breeds. Most of our improved breeds 
exhibit more than one type entirely aside from considerations 
of sex. For example, the Hereford is remarkably constant in 
color, but there are two distinct types as to form. One is heavily 
built and long-bodied, with deep flanks and straight thighs ; the 
other is smaller and shorter, with less depth behind and a 
tendency to rounded buttocks. The fore quarters are not differ- 
ent in the two types, but the differences behind are marked 
and the types do not readily blend. The breed appears to be 
almost, if not entirely, dimorphic. 

Among the Shorthorns we have no less than half a dozen 
types that do not readily mix. The pure white is distinct in con- 
formation, as is the Duchess roan, the Cruickshank roan, the 
cherry red, the dark mahogany red, and the Cruickshank red. 

The Percheron horse is dimorphic both as to color and as to 
form. Whether it will always remain so, or will finally blend 
into a common type as to color and conformation, time only 
will tell. The same is true of the Jersey and the Holstein- 
Friesian cattle, the Berkshire hogs, and the Shropshire sheep. 

All widespread and most newly developed breeds are polymor- 
phic, — the first from the external influences and different stand- 
ards of selection, the second from recently associated dissimilar 

^ Excellent material on seasonal dimorphism of butterflies may be found in 
Weismann, Studies on the Theory of Descent, I, i-ioo; and on polymorphism in 
insects, Ibid. II, 401-481. 



478 TRANSMISSION 

characters (see Mendel's law). Whether, in good time, they 
will blend, or will remain distin?t, giving rise to polymorphic 
forms within the breed, is an important question in which the 
breeder is always deeply interested. If the polymorphism can 
be removed, he of course desires to do it ; if not, he must make 
the best of it and cease wasting time over the unattainable. 

In all such cases the breeder is to satisfy himself as quickly 
as possible whether the polymorphism is temporary or perma- 
nent ; and if it be permanent, he will do well to choose the 
type he is to breed, and abandon the effort to blend it with 
another, — in other words, he must be content to secure his 
results gradually, by selection. 

SECTION II — STATISTICAL METHODS OF STUDY OF 
HEREDITY 

Until recently no phase of evolution has been so badly studied 
as heredity. The common mistake has been to note a few 
remarkable individuals and exceptional instances, and from 
these attempt to deduce the "laws of descent." In this way 
popular conceptions of heredity have grown up, many of which 
are exceedingly erroneous, not to say fantastic. 

We have only recently learned that studies and conclusions 
based upon individual instances are worse than useless because of 
the extreme range of variability, and that to determine the facts 
of heredity with any degree of reliability, we must study tlic race as 
a tuholc, and not simply the separate individuals that compose it. 

All this means that the laws of descent are to be discovered 
by a critical study, not of individuals, but of entire populations, 
or at least of proportions of populations sufficiently large to be 
safely representative. 

Unfortunately, the application of the statistical method to the 
study of this subject is comparatively new, and as it is extremely 
laborious, the accumulation of a large mass of material will of 
necessity be a sorhewhat slow process.^ 

1 Gallon was the first to apply present-day methods to the study of heredity, 
but Pearson and others followed, and a considerable literature is accumulating, 
to which important additions are being rapidly made. The quarterly journal 
BioDictrika is devoted to the study of this subject by the statistical method. 






HEREDITY 



479 



Unfortunately again, the first and most exhaustive studies 
were made outside of our field, and mostly in that of human 
characters, so that the best material for the study of heredity 
lies in this field. But later studies, in wider fields, lead us 
confidently to believe that the same general principles control 
transmissions everywhere, in all races and with all characters. 
Accordingly the writer will employ any studies that have been 
made, in whatever fields, that offer valuable material either for 
elucidating principles or for illustrating methods of study. The 
fullest data of all are those collected by Galton, dealing princi- 
pally with stature, and they will be freely employed for both 
purposes. 

SECTION III— THE REGRESSION TABLE 

As already seen (chap, xii), when a representative popula- 
tion of any race is arranged in the form of a frequency distribu- 
tion we are able to deduce exceedingly accurate expressions for 
variability. 

If now this distribution be separated and assorted according 
to parcjitage, we shall have a series of distributions, each of 
similar parentage, the whole presenting the best facilities possi- 
ble for the study of heredity. Such a tabular arrangement con- 
stitutes what is called a " regression table," and inasmuch as 
all regression tables present the same general features, we look 
upon them with confidence as affording reliable data for the 
study of this most important but otherwise most difficult and 
apparently self-contradictory subject. 

In all regression tables a scale of values (measurements, 
weights, numerals, or other valuation) is provided at one side 
for the parents, and a corresponding scale along the top for the 
offspring, or vice versa. ^ 

The offspring, considered as adults, is then distributed, each 
individual being recorded opposite the value representing his 

1 Obviously the parental measurements may be arranged along the top and 
those of the offspring at the side. Every observer follows his fancy in this 
respect, and as a matter of fact the tables are made in both ways. The writer 
has become more accustomed to the one described in the text, and for no other 
reason prefers to arrange the parental values at the side. 



48o 



TRANSMISSION 





^ 


■<; 


■^ >; 


•^ V^ b< <? ■>« <s "^ S 


5i 


^ 


iS 

Means 

of 

Children 


■ ^ + 






17 
Number 

Mid- 
Parents 




p- n T^ ^ ro ci w 


"-1 



ri 


ten 

00 



16 
Number 

Adult 
Children 




" M N 


00 
ri 


tort 

06 


^ 


> 

• ■* f 

< ■ 






■* 




ro "^ ■ 










M ... 

2" ro "^ ^' '■' "^ "* "^ 

r^ ... 






r^ 


PI 
d 


:? 








1-1 


d 


2 




M ^ r^ 00 M ■ M 

CI 1-1 M 








ON 

\0 


- 


d 


1-1 Tj-U^ii ON^l^ 
I-c ►- n M M. 






On 
OS 


On 







M "-1GO rococo rOt^M 1-1 
" ro -rr ro " 


-0 


00 


0- 




i-irOMO^00-*r^ ■►-< 
1-1 PI ro M " 







co 




• ■<j-ror^~00 r^" "oci 

ci n ro " 1-1 


00 
ro 


On 


l^ 




i-i CI ro i-< >-i 


r^ 




vD 




• >-«-tj-\OLorit^.-ii-i 


% 


00 


^ 






' VO 1-1 '^f "-> u^ ■^ tT 


ON 


00 
r^ 


'* 






11 i-c t-^ "^ ro O^ Tf- M 


PI 


00 


^ 


ri 




' ro ro ' w 


r-- 


VO 

vd 

VO 


« 


13 

pq 




• • 


"-) 




- 




0. 
> 

c 
< 




d On CO r^ vd 10 T] 

vj-aij^ do sj-HOiajj 


'1 







en 

C 



(1) VO 



O QJ 

>^2 



C ^ *; cu 



a 


^ 


vD 




n 


hi 




bfi 


C 


c 


<i) 




rt 


-C 


T 






•a 




S - £ s 



ri O 






HEREDITY 48 1 

parent and in the column representing his personal value as to 
the character under question. When completed, such a table 
will show the number of offspring of each particular value, and 
also the kind of parents from which they sprung. 

In whatever direction its parts are read, such a table consists 
of frequency distributions whose means and standard deviations 
may be determined by the methods already given. The horizontals 
show the distribution of offspring of like parents, the verticals 
show the range of parents capable of producing like offspring, 
and the totals represent the respective generations. 

One of the first tables of this kind published, and one of the 
best for our present purposes, is the one on the preceding 
page, from Galton, based on his studies of the stature of Eng- 
lish people.^ 

1 See Galton, Natural Inheritance, p. 208. 

In this table the heights were taken in small fractions, but recorded in i-inch 
groups. For instance, all measurements falling between 66 and 67 inches he 
recorded as 66.5. In attempting to do this for the sons, however, he noticed "a 
strong bias in favor of the integral inches." Hence he adopted for these 
measurements 66.2, 67.2, etc., instead of 66.5, 67.5, etc. As a matter of fact, 
it makes little difference what scale is adopted, provided the same plan is always 
observed in the matter of discarding or of recording fractions. 

One slight inaccuracy for the individual in the long run offsets another, and as 
a whole such adjustments do not interfere with results. Trial calculations, too, 
will show that measurements taken an inch apart give substantially the same 
results as when taken a half inch or a quarter inch apart. 

In this table the heights of the adii/t children are compared with the heights 
of the 7)iid-pare)its ; that is, with the average height of the father and the mother 
after multiplying the mother's height by 1.08, because women are, on the 
average, one twelfth shorter than men. All female heights are, therefore, " trans- 
formed " and recorded as male heights. This custom is observed in all statistical 
studies involving sex ; that is, the female values are reduced to their " male equiv- 
alents," so that sex differences are eliminated from the mid-parent, or, more prop- 
erly speaking, everything is reckoned in terms of males. 

Early in his studies the question arose whether the mid-parental height is a 
safe basis ; that is to say, whether the child of one tall and one short parent is, in 
general, the same as the child of two parents whose heights are equal, but whose 
average height is the same as the average height of the tall and the short parent ; 
in other words, would the children of a 70- and a 64-inch parent (average 67 inches) 
be the same as one of two parents each of whom is 67 inches in height ? 

After the study of many cases Galton found no difference. He therefore con- 
cluded that a perfect blend takes place in respect to stature, and that the mid- 
parental height, after making due allowance for sex differences, may be safely 
taken as the true height of the mid-parent for purposes of heredity studies (see 
Natural Inheritance, pp. 88-90). We have since learned that for extreme accuracy 



482 TRANSMISSION 

It is not likely that all characters behave precisely as does 
stature, — indeed, it is known that they do not ; but all studies 
go to show that characters of every kind obey the same general 
laws in descent, and all regression tables that have ever been 
prepared exhibit the same general features.^ This table, there- 
fore, while primarily for the study of stature, may be considered 
as typical of regression tables, and deductions made from it, 
agreeing as they do with those made from all other similar 
tables, whatever the race or the character, may be safely 
accepted as exhibiting fundamental laws in heredity. Because 
all regression tables afford the same deductions, they may be 
stated in the form of general principles as outlined in the 
following: sections. 



SECTION IV — LIKE PARENTS BEGET UNLIKE OFFSPRING 

AND, CONVERSELY, LIKE OFFSPRING MAY BE 

BEGOTTEN BY UNLIKE PARENTS 

In this table the heights of the parents are in the rows b to in, 
and those of the children (as adults) in the columns 2 to 15. It 
will be seen at once that the offspring of parents of any given 

slight modifications are necessary on account of the parental ancestry, but such 
corrections are not necessary for present purposes. 

Galton calls attention to an error in the first row of children and mid-parents, 
saying that an error was introduced somewhere in the original tables, which cannot 
now be corrected. " It is obvious that four children cannot have five mid-parents," 
he says, but the numbers are so small as to be generally discarded, and hence the 
table is reproduced, error and all. He adds : " The bottom line (fourteen children 
with one mid-parent), w"hich looks suspicious, is correct " (Natural Inheritance, 
p. 208). 

In calculations generally the extremes (above 72.5 or 73.2, or below 64.5 or 
63.2) are discarded because the numbers are small and because exact measure- 
ments are not given. In calculating the general mean, however, two values have 
been determined, one without the extremes, .the other by including the extremes, 
assuming that measurements above 73.2 averaged 74.2, above 72.5 averaged 73.5, 
below 64.5 averaged 63.5, and below 62.2 averaged 61.2. The assumption is 
entirely gratuitous, but it affords a basis for using the extremes, although, as is 
noticed, it makes but slight difference in the results. 

1 Regression tables may be prepared for any character that can be measured, 
weighed, counted, or in any way accurately determined. It only happens that 
studies in human stature have been the most complete of any, and are, therefore, 
used here. 



HEREDITY 483 

height are not the same, but, on the other hand, that they con- 
stitute a distribution beginning be/ow the parentage, and extend- 
ing to a considerable distance above it, with the largest number 
of individuals near the middle of the distribution, close to but 
not identical with parental height. 

Thus the 68 children of 22 parents 70.5 inches high (row e) 
are distributed from below 62.2 to above 73.2 inches, a range of 
II inches, with the greatest number (18) slightly below the 
parental height (70.5). Any other row taken at random will show 
the same distribution in the stature of the offspring. Heredity, 
therefore, involves something besides the influence of the imme- 
diate parent, which, according to all studies, seldom exceeds 50 
per cent of the total influence of the ancestry, leaving the other 
half to be accounted for by ancestors farther back.^ 

Not only is it true that like parents produce unlike offspring, 
but the converse is also true, — that like offspring may result 
from unlike parents. Take any column of the table at random, 
as column 10, containing the distribution of the 167 children of 
the uniform height, 69.2 inches. These men of even height 
were produced by parents ranging in stature all the way from 
72.5 inches down to less than 64.5 inches, — a range of 8 
inches. To be sure, the parental height that produced the 
greatest number (48) was 68.5 inches, not far from the common 
height of the offspring (row <?, column 16) and almost exactly 
the average height of all the parents (row ^, column 17), but 
the critical study of this and all the other columns will clearly 
show that the same kind of offspring may be produced by 
greatly different parents. 

These facts show clearly that two sires or dams of equally 
favorable appearance may have sprung from very different 
ancestry. They both belong to a distribution covering a con- 
siderable range, and if our selection is to be effective we need 
to know everything possible of the entire group to which the 
prospective parent belongs, or at least be intelligent as to the 
portion of the distribution from which he is drawn. 

^ Every individual of bisexual parentage has a total of 2046 ancestors within 
ten generations. Whether these ancestors represent that many different individ- 
uals, or whether some are oft-repeated, depends upon the closeness of breeding. 



484 TRANSMISSION 

SECTION V — REGRESSION. IN GENERAL, THE OFF- 
SPRING IS MORE MEDIOCRE THAN THE PARENTS; 
THAT IS, WHATEVER THE PARENTAGE, THE OFF- 
SPRING EXHIBITS A STRONG TENDENCY TO 
REGRESS TOWARD THE MEAN OF THE RACE 

A glance at any regression table shows an uneven distribu- 
tion of the population, with the largest numbers near the middle 
of the table, exhibiting a strong tendency to cluster about the 
center. Not only is this so, but if any parental row {c to ni) be 
carefully studied, the following points will be noted : 

1. The mean or average heights of the children (column 18) 
are in no case the same as the heights of the parents. Compare 
column 18 with column i. 

2. When the parental height is above the mean of the race, 
that is to say 68.5 inches and upward {c to g), then the mean 
height of the children is something less than the height of the 
parent (see any row from c to ^). 

3. But when the parental height is below the mean of the 
race, — 67.5 inches and less (// to ;;/), — then the mean of the 
children is greater than the height of the parent (see any row 
from // to ni). 

To illustrate : in row e are recorded the heights of the 68 
children of 22 mid-parents 70.5 inches high. In column 18 we 
see that the 7nean height of these 68 children was 69.5 inches, 
or a height one inch beloiv the parentage, and by that much 
nearer the general mean of the race. Again, in row k are 
recorded the various heights of the 66 children of 1 2 mid-parents 
65.5 inches tall. In column 18 we see that the mean or average 
height of these 66 children was not 65.5 inches, as in the case 
of the parents, but 66.8 inches, or 1.3 inches greater, and by that 
much nearer the general mean of the race than were the heights 
of their parents. 

This principle of regression, or, as it is sometimes called, the 
"drag of the race," represents the "pull" of the ancestors 
beyond the immediate parents. By this we see that, on the 
whole, offspring are less exceptional than their parents ; or, 



HEREDITY 485 

stated in general terms, that the tendency is toward mediocrity, 
and that offspring are, on the whole, more mediocre than their 
parents. This is so because, /;/ the absence of selection, the two 
thousand or more near-by ancestors, all exercising some influ- 
ence, were, altogether likely, about an average lot, and their 
pull is strong toward mediocrity. With rigid selection the aver- 
age could be greatly raised, making the pull higher ; but this 
results simply in raismg the level of mediocrity, and the principle 
would still hold ; for it is beyond hope or expectation that these 
two thousand or more ancestors could ^//be held at a high level. 
This is why breeders generally find many disappointments in 
breeding from exceptional individuals, — their offspring cannot, 
on the average, be equal to themselves. 

On the other hand, the offspring of the inferior parent is 
helped by the principle of regression, which in this case acts as 
a " boost " instead of a " drag," ^ and we hear of such a parent 
that he " breeds better than himself," — all of which is a credit 
to the ancestors if not to the individual. However, the children 
of tall parents, while not so tall as their parents, are yet taller 
than the children of short parents, giving rise to the peculiar 
form of the regression table known as its " skew." 

This principle of regression through the influence of the 
ancestry beyond the immediate parent, and the essential medi- 
ocrity of the offspring as compared with the parent, are then 
well established. This is not from any inherent superiority in 
parents or inferiority in offspring, but from the fact that medi- 
ocrity is the common condition of the bulk of the race. 

No remedy for regression. Nothing but long-continued selec- 
tion can ease the race from the drag of regression, and even 
then, and always, the offspring are still subject to the pull of a 
new but higher mediocrity. 

1 This principle is the salvation of the " submerged fraction " of humanity, and it 
is the principal reason why so many successful, even self-made men, spring from 
unpromising parents. It is entirely possible when the ancestry has been only 
recently submerged ; it is hardly possible when there is a long line of criminal or 
defective ancestors. 

A distinction is to be made, on the one hand, between the children of poor and 
honest parents who lack advantages but whose blood lines may be excellent, and, 
on the other hand, those whose ancestors have been submerged for generations ; 
very few of these rise to prominence, or, indeed, can rise. 



486 TRANSMISSION 

This mediocrity is, therefore, a thing always to be reckoned 
with by the breeder who hopes to attain uniform success with 
improved strains. He cannot free himself from its influence. 
We shall see that its pull is not less than 50 per cent. The fail- 
ure to know this fact, and the willingness to rest the case with 
the immediate parents and to assume that " like father like son " 
is the way of heredity, or to accept /;/;7Vj/ of blood (pedigree) as 
synonymous with unifonnity of type, — this is the one fertile 
cause of the greatest failures in stock breeding. The only sure 
basis of uniform success lies in a uniformly excellent ancestry 
for at least five or six generations back.^ Then the "drag of 
the race " will become a friend and not an enemy of improve- 
ment ; but, no matter how excellent the ancestry, it can never 
equal the exceptional parent. In order to make the most of him, 
therefore, this drag should be reduced to a minimum. 

SECTION VI — THE MEASURE OF HEREDITY 

Now this regression is the pull of the ancestry back of the 
parent, and it is the best argument for the fact that inheritance 
is partly from the race and not exclusively from the immediate 
parent. Clearly, we need a measure of the degree of resemblance 
between the offspring and the immediate parent, so that we may 
know how much to credit to the parent and how much to credit 
to the back ancestry through regression. Such a measure of 
resemblance between mid-parent and offspring will be a good 
measure of heredity, and it is called the coefficient of heredity. 

The coefficient of heredity. Fortunately this involves no new 
conceptions and no new methods. The' regression table is noth- 
ing more nor less than a special form of correlation table in which, 
instead of involving two characters in the same set of individuals, 
we seek the correlation between two sets of related individuals 
zvith respect to the same character. 

Thus, in the table of statures, we have in fact a correlation 
table between mid-parents and sons with respect to stature, and 
its correlation coefficient (r) ^ \s> for them a coefficient of heredity. 

1 See Law of Ancestral Heredity, sect, xiv of this chapter. 

'■2 The coefficient of correlation i.s everywhere denoted by the letter r. 



HEREDITY 487 

The coefficient of heredity is therefore nothing more nor less than 
the correlation coefficient (r) obtained from a regression table 
in which two sets of individuals related by descent are tabulated 
with respect to the same character. The methods of finding 
the coefficient of heredity are precisely the same as those already 
described for finding the coefficient of correlation ; indeed, the 
correlation coefficient of a regression table is the coefficient of 
heredity. 

It is manifest that this correlation table may be constructed 
not only between mid-parents and offspring, but between fathers 
and sons, between grandfathers and grandsons, between mothers 
and sons (or daughters), between uncles and nephews, between 
brothers and sisters, between brothers and brothers, and, indeed, 
between persons connected by any ties of consanguinity what- 
ever, direct or indirect. In each case the correlation coefficient 
becomes a good measure of hereditary resemblance. 

If a regression table be constructed between fathers and 
mothers, a correlation would still be found, though the two are 
united by no blood lines except those common to the race in 
general. Such correlation comes entirely through selection, and 
its coefficient (r) is commonly called the coefficient of cross 
heredity or " assortative mating." It is a good measure of the 
degree of selection involved in mating. 

The table on the next page gives some of the coefficients of 
heredity that have been determined for different relatives. 

Pearson remarks : "We see that on the average the intensity 
of parental correlation is about 0.3 to 0.5 ; of grand parental, 
about 0.15 to 0.3; and of fraternal, about 0.4 to 0.6, — the 
latter correlation being somewhat reduced when the fraternity 
consists of members of opposite sexes." 

Regression coefficient. The regression coefficient here is 
computed exactly the same as the regression coefficient from 
any other correlation table, and it has the same uses, namely for 
prediction ; that is to say, for example, knowing the deviation of 
a group of mid-parents from their mean, what deviation shall 
we expect on the part of their offspring .-* 

The use of the word "regression" in the term "regression 
coefficient " is likely to lead to confusion. We must not assume 



488 TRANSMISSION 

Coefficients of Heredity for Different Relationships ^ 



Relationship 



Father and son 

Father and daughter . . 

Mother and son 

Mother and daughter . . 

Mother and son 

Mother and daughter . . 

Sire and foal 

Dam and foal 

Grandsire and offspring 
Grandsire and offspring 
Brother and brother . . 
Brother and brother . . 

Colt and colt 

Sister and sister 

Sister and sister 

Filly and filly 

Brother and sister . . . . 
Brother and sister . . . . 

Colt and filly 

Whole brethren 



English 

English 

English 

English 

North American Indians 
North American Indians 
Thoroughbred horses . . 
Thoroughbred horses . . 
Thoroughbred horses . . 

Basset hound 

English 

North American Indians 
Thoroughbred horses . . 

English 

North American Indians 
Thoroughbred horses . . 

English 

North American Indians 
Thoroughbred horses . . 
Basset hounds 



Character Correlation 


Stature . . 


396 


Stature . . 


360 


Stature . . 


302 


Stature . . 


284 


Head index 


370 


Head index 


300 


Coat color 


517 


Coat color 


527 


Coat color 


335 


Coat color 


134 


Stature . . 


391 


Head index 


379 


Coat color 


623 


Stature . . 


444 


Head index 


489 


Coat color 


693 


Stature . . 


375 


Head index 


340 


Coat color 


583 


Coat color 


508 



that the coefificient of regression is a direct measure of the pull 
of the back ancestry, or that it directly measures the dissimilarity 
between parent and offspring as shown in the regression table. 
In fact, we note that when regression is perfect, then the coeffi- 
cient of regression is zero ; and when there is no regression 
(perfect correlation), then the regression coefficient is large. 
This is brought out in the diagram on the following page. 

This diagram is a geometrical exhibit of the regression table 
of statures (page 480) It is simply a reproduction of that table, 
omitting the frequencies and putting in crosses (x) to repre- 
sent the means of the horizontal arrays ^ (column 18). 

1 Pearson, Grammar of Science, pp. 458-460. 

2 The mean of offspring in this table is 68 inches, and we have assumed this 
value to be, for the present purpose, near enough to the mean of mid-parents and 
of the race to take the horizontal and vertical Unes marked 68 as passing through 
the mean of the table. 



HEREDITY 



489 



If there were no regression, that is, if the offspring followed 
fully the lead of the parent, then parents above the mean would 
have offspring equally above the mean ; that is to say, parents 
69 inches high (one inch above the racial mean) would have 
children also one inch above the mean, and parents two inches 
above the mean would have children also two inches above the 
mean, or 70 inches in height. In this way, were there no 

GS 





62.2 


63.2 


64.2 


65.2 


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66.2 


hts 
67.2 


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:hilch 
70.2 


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71.2 


72.2 


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Fig. ^5. Diagram representing regression 



regression, these points would lie in a line M'OM, with a devia- 
tion of 45° from the vertical. 

But regression is a fact, and the children of 70-inch parents 
are not 70 inches tall but something less, and so on for other 
values ; so that, when the true means are platted as calculated 
from the horizontal arrays of the regression table, and then 
connected by the best-fitting straight line, this line A""' (9 A^ does 
not coincide with M'OM, as it would were there no regression. 
This is known as the regression line, and its slope is the 
measure of the pull of parental heredity. The measure of this 



490 TRANSMISSION 

slope is our coefficient of regression, and its value is expressed 
by the ratio of PN to PM. 

Galton ^ finds this ratio, when dealing with mid-parents and 
mid-filial statures, to be approximately as 2 to 3 ; " that is to 
say, the filial deviation from P (the common mean) is on the 
average only two thirds as wide as the mid-parental deviation. 
I call this ratio of 2 to 3 [he says] the ratio of ' filial regression.' 
It is the proportion in which the son is, on the average, less 
exceptional than his mid-parent." That is, the deviation of the 
stature of children from the mean of the race is only about two 
thirds as wide as that of their mid-parents. 

SECTION VII— THE MEAN OF THE OFFSPRING NOT 

NECESSARILY THE SAME AS THE MEAN OF 

THE PARENTAGE 

At first thought it would seem axiomatic that, on the average, 
the offspring as a whole would be the same as the parents, 
unless the race is undergoing change. In the table of statures, 
hovjever, by comparing columns 16 and 17, row 0, we see that 
the! mean of all the parents was 68.6 inches (not counting ex- 
tremes, or 68.7 inches including extremes), while the mean of 
the adult children was but 68.0 inches (68.1 inches including 
extremes). This indicates a loss in stature of over a half inch 
in a single generation, unless some other influence is at work to 
counteract this discrepancy. That counteracting influences are 
at work we shall shortly discover, but the fact remains that the 
mean of the offspring is seldom identical zvitJi the mean of the 
parentage. This fact is to be construed as meaning one (or both) 
of two things, — either that the race is undergoing transforma- 
tion, or else that all grades are not equally productive. 

In this connection it is to be noted, first, that 68.6 is not to 
be taken as the mean of W\q. generatioti to which these mid-parents 
belong ; that mean might have been either less or more, because 
not all members of a generation become parents, nor is the 
parent population a random draft from the generations of the 
mid-parents. 

1 Galton, Natural Inheritance, p. 97. 



HEREDITY 49 1 

No fact is better known among statisticians than that wives 
differ from daughters and mothers differ from wives, — which 
means that all women (daughters) do not marry, and that not 
all wives are mothers (selection) ; that is to say, parents are 
a selected draft from the entire population, and we should not 
expect to find their mean the same as that of their offspring, 
which closely approaches that of the general population. 

SECTION VIII — EXTREMES OF A RACE RELATIVELY LESS 
PRODUCTIVE THAN THE MEANS 

In the table of statures a strong tendency is evident toward 
increased height and a still stronger one toward decreased 
stature (see sect, ix, " Progression "). This being true, the racial 
distribution would rapidly spread, if not entirely divide, into two 
races, giants and dwarfs, unless prevented by some principle such 
as natural selection. This principle in this particular instance is 
evidently relative infertility, a principle easily deduced in at 
least two ways : 

1. One hundred and three children are recorded at or below 
64.2, and only one parent below 64.5 (see table of statures). 
Clearly most short children do not become parents, else the race 
would rapidly degenerate as to size. This agrees with common 
observation, which is that dwarfs do not marry. When, however, 
the principle is applied to degeneracy and crime, the case is dif- 
ferent, for criminals often produce more than their normal ratio, 
and many of their offspring, by the principle of progression 
(see sect, ix), are frightful degenerates. 

To what extent giants marry is not so clearly indicated by 
this table, but that they are less fertile than the average when 
they do marry is clearly shown by comparing columns 16 and 17. 

2. The average of fertility in this table as a whole is almost 
exactly 4^ (928 -r- 205) per mid-parent. This average is well 
sustained in the lower and middle statures, rising in many 
cases to 5 per mid-parent ; but it rapidly lessens in the higher 
statures, for from 70.5 up it is approximately 3. This, too, 
agrees with common experience, namely, that extremes of a race 
are generally less fertile than the means. Indeed, it is commonly 



492 TRANSMISSION 

fertility that fixes type, unless its effects happen to be overcome 
by some other form of selection ; that is to say, the type of 
highest fertility will become most numerous, and will therefore 
naturally determine the type of the race. 

It is evidently the lessened fertility on the part of extremes, 
and the higher breeding powers of the mediocre individuals, 
that in nature assist selection in holding the principle of pro- 
gression in check, thus generally, but not always, preventing 
the splitting up of races into smaller varieties ; indeed, type is 
mainly the resultant of relative fertility and selection, — very 
largely of the former. This is why breeders of highly improved 
races must needs look well to fertility, for at that point their 
first troubles will arise, all regression tables indicating that they 
will never suffer from lack of variability, as seen in the following 
section. 

SECTION IX — PROGRESSION. PARENTS IN GENERAL PRO- 
DUCE A FEW INDIVIDUALS MORE EXTREME 
THAN THE RACE 

What is true of averages is not necessarily true of individuals 
or of selected groups. Regression applies to the mass, not to 
the separate individuals that compose it.^ 

Parents in general produce individuals both inferior and 
superior to themselves, forming a frequency distribution whose 
mean lies somewhere between that of the parent and the general 
mean of the race. But the individuals extend both ways from 
this mean and some of them lie well beyond the range repre- 
sented by the parentage. On this point see any row in any 
regression table, as row e in the table of statures (page 480). 

For example, in the case at hand, but 5 mid-parents, and pos- 
sibly only 4 (10 or 8 parents), are above the height 72.5 inches 
(see row b), but 31 children are recorded at 73.2 or above (see 
columns 14 and 15). The number of extreme children is thus 
more than three times as great as the number of extreme 

1 For example, we have shown that, on the average, offspring are more mediocre 
than their parents ; but for a highly selected offspring (72inch stature) we should 
find the parents to be nearer mediocrity than the offspring. 



HEREDITY 



493 



parents, even with the handicap of 0.7 inch, and only 3 of them 
were born of extreme parentage (row /;, cokmin 14). Not only 
*i^ that, but the upper limits of height in this table are decidedly 
with the children rather than with the parents ; in other words, 
children can be found taller than any parent. 

At the other extreme of the table, but 6 mid-parents are 
recorded at or below 64.5, but no less than 103 children are 
recorded at 64.2, or below. 

All this goes to show that, notwithstanding the principle of 
regression, the child population extends over a much wider 
range than does the parental, — a fact made clearly evident by 
comparing the offspring (row ;/), extending from below 62.2 to 
above 73.2, with the parents (column 17), extending only from 
below 64.5 to above 72.5. While neither of these ranges fixer, 
the limit, yet the range of the offspring is clearly the greater. 

Viewed from any standpoint, offspring cover a wider range of 
variability than their parents, and some of them lie quite beyond 
the limits of parentage. This is progression, and its effect is, 
especially in the case of extreme parents, to send some indi- 
viduals not only beyond the limits of parents but well beyond 
the former limits of the race. The practical effect is that the 
population of any race can be moved either up or down through 
a large range, and either limit extended at will by the use of 
highly selected parents. 

The behavior of a race under rigid selection and the operation 
of the principle of progression are well illustrated by the table 
on the next page, the data for which came from the records of 
ten years of corn breeding by Dr. C. G. Hopkins, of the Agri- 
cultural Experiment Station of the University of Illinois. In 
these experiments the purpose was to influence the protein 
and the oil content of corn by selection. It is notable in this 
connection that all four strains, — high-protein, low-protein, 
high-oil, and low-oil, were developed from the same founda- 
tion stock. 

This table is taken from the experiments in breeding for 
increased protein in corn.^ It will be noted that the foundation 
stock of corn (1896), mixed ancestry, showed an average of 

1 Bulletin No. ii6, Agricultural Experiment Station, University of Illinois. 



494 



TRANSMISSION 



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HEREDITY 495 

10.92 per cent, with a mode of 1 1, and an upper limit (one ear) 
of 14 per cent, — more accurately 13.87. 

The result of one year's selection made little evident impres- 
sion. The second year's crop was not much better. The mode 
was the same, the average slightly lower, but the distribution 
became somewhat extended, with the appearance of two higher 
values represented by one ear each. 

In the third year, with still better seed (13.06), the distribu- 
tion extends still farther, but the new value is dozvji, not up. 
We note, however, a general increase of the higher values, and 
the mode has moved up a notch. ^ 

In the fourth year (1900), with still better seed (13.74), the 
lower values lessen and some drop off entirely. One new value 
appears. All the upper frequencies are increased ; the mode 
has gone up two notches, and we now have no less than 28 ears 
as good or better than the extreme ear of 1896. 

The same principle continues in 1901, which was an excep- 
tionally good year for protein, and the theoretical mode goes up 
nearly t/ure points, reaching a par with the single exceptional 
ear of the foundation stock. It so happens that this year the 
number of ears examined was the same as that of the foundation 
stock (163), and of these ears no less than <^7, or 28 per cent, zvere 
tJie equal of the exceptional first ear. The effects of selection 
settle back slightly the next year, but in the succeeding season 
lost ground is recovered and there is produced the exceedingly 
exceptional ear, 17.33, which has since proved a remarkable 
parent. 

The principle of progression is still further illustrated by the 
next table, showing the effect of selection botJi xvays. This is 
taken from Dr. Hopkins's original data in breeding for high oil 
and for low oil from the same foundation stock. The student 
should note the decisive manner in which these generations 
separate themselves from the foundation stock and from each 
other as selection goes on. Nothing could show more conclu- 
sively that under intense and persistent selection new values 
appear freely as the race becomes liberated from the heavy drag of 

1 It can be seen by inspection that the theoretical mode is not so high as the 
empirical mode, 12. 



496 



TRANSMISSION 














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HEREDITY 497 

mediocrity, — all of which requires several years, and accounts 
for the comparatively small effects of the first one or two years' 
selections. 

The same principle is evidently present and at work in stature 
(see table, page 480), for we note that the children cover a wider 
range than do the parents. It might seem that under the prin- 
ciple of assortative mating these exceptional children would break 
away and establish a race of giants and one of dwarfs. We are 
acquainted with some of the causes that prevent this ; namely, 
relatively small fertility in giants (see table) and lack of marriage 
among dwarfs. As it is, however, the mean of stature is some- 
what above the highest fertility (see table). 

It used to be said that the offspring is a kind of mean of the 
parentage, and that the most that could be accomplished by 
selection was the production of fewer mediocre and inferior and 
a larger proportion of superior individuals. ^ We know now, how- 
ever, that the great bulk of the population will always be medio- 
cre, but that by extreme selection we may secure new upper 
values quite beyond former limits, not only of the parents but 
of the race, and that at the same time the entire population will 
respond to an upivard trend, thereby raising the level of mediocrity. 

All experience in breeding agrees with the principle here set 
forth. At the University of Illinois, when experiments in corn 
breeding were first undertaken, the question arose whether the 
results of the first year or two were anything more than assorta- 
tive. The effects of selection were not at first pronounced, 
owing, of course, to the "drag" of previous ancestry. But 
selection was extremely rigid, — a fact which rapidly freed the 
back ancestry from this drag, — and with this came a decided rise 
in the mean of the crop ; that is to say, the standard of medioc- 
rity was raised, and along with this their appeared from time to 
time occasional cars with values far above anything ever foimd 
in the foundation stock. These were new values due to the prin- 
ciple of progression, and the fact that the coefficient of variability 

1 This position was always untenable, because, given the two best parents in a 
race, if the offspring is a mean between the two then no offspring can ever equal 
its better parent. How then was the superior parent produced .'' Such a doctrine 
has but one outcome, the bringing of the total population to a dead level of 
mediocrity. 



498 TRANSMISSION 

is not now growing less (see chap, xii) leads to the conclusion 
that the upper limits in this breeding experiment will be set by 
some factor other than the failure of variability ; indeed, it is 
the opinion of the writer that the principle of progression is able 
always to afford all the material the breeder will need, and that 
the limits of improvement will be set, when they are set, by 
some biological, mechanical, or other considerations entirely 
aside from the failure of variability to present new upper values 
on which to base selection.^ The remarkable fact about progres- 
sion is that the distributions are not distorted but are all typical 
of the race (see table, page 496). 

This fact of progression betrays a unique principle in heredity, 
or rather in variability, because progression is over against and 
in spite of the "drag of the race." Those individuals that have 
overleaped the limits of the race have not only exceeded their 
own parents, but by nmcJi more have they exceeded the compara- 
tive mediocrity of their other ancestors. ^ Progression cannot, 
therefore, be explained by any principle of " mean parentage." 
It rests upon a principle fundamentally distinct, and is to be 
regarded as the result of those fortuitous combinations of physio- 
logical units which we may expect to occur from time to time in 
the complicated processes attending reproduction and differenti- 
ation, and on which more will be said in Section XII of this 
chapter. 

This suggests what will be later found to be a fact, namely, 
that in a large sense heredity follows the laws of probability, and 
in process of time we may expect all possible combinations of the 
elements that make up characters, and of the characters that 
make up the race, the largest proportion of which will cluster 
about a common point, which we call the type, but a few of 
which will inevitably appear at the extreme limits of the range 
of possibilities. 

1 The greatest menace to extreme improvement is, as has already been said, 
lessened fertility. According to Pearson all evidence points to the fact that varia- 
bility will never be reduced by more than about 1 1 per cent. See Grammar of 
Science, p. 483. 

2 The student will not fail to note that the ancestors of the exceptional parent 
are of necessity more mediocre than that parent. They will then exert their influ- 
ence against, not in favor of, progression. 



HEREDITY 499 

SECTION X— THE EXCEPTIONAL INDIVIDUAL ARISES 

EITHER FROM MEDIOCRITY OR FROM THE 

EXCEPTIONAL PARENT 

Further inspection of the table of statures shows that of the 
72 children recorded above six feet in height (see columns 13, 
14, 15), 42, or over one half, were produced by mid-parents 
70.5 inches or under; that approximately 22 were produced by 
mid-parents less than one inch above the mean of the race ^ 
(68.6 inches, see row o, column 17) ; that no less than 12, or one 
sixth of all, were produced by mid-parents recorded at or below 
the mean of the race; and that i was produced by a 65.5-inch 
mid-parent. 

From this we see that exceptional individuals may arise either 
from exceptional or from mediocre parents. The probability, 
however, is greatly in favor of the former. Six 72.5-inch mid- 
parents produced 13 exceptional children out of a total of 19, 
considering everything above six feet as exceptional. Of this 
number 6, or over 30 per cent, exceed their own parents in 
height. Though the 69.5-inch mid-parents produced a higher 
number of exceptionally tall children (20), 41 parents were 
involved instead of 6. This is less than 3 per cent of the total 
children (183), instead of 68 per cent, as in the case of the 
progeny of the taller parents. 

It is at this point that the political scientist and the threm- 
matologist recognize different principles. Both are interested in 
exceptional individuals. As we have seen, they may be had 
either from the general population or from a highly selected 
parentage. The breeder chooses the latter because he cannot 
afford to support so large a population for so few exceptional 
individuals. He takes the highly selected parentage because 
the proportion of extreme excellence is higher, and because its 
"drag" is less. He is desirous of using minimum numbers for 
economic reasons. 

The political scientist is limited by no such considerations. 
If he resort to selection (election) each time a ruler is to be 

1 Including only one half of the offspring produced by parents recorded at 
69.5. 



500 



TRANSMISSIOJ^ 



chosen, he will always have good material at hand, and, as he is 
not specially interested in progeny, he is not concerned with the 
"drag." 'VJh^X he. w^.nX'^i \?, iiidnndital service. 

If, on the other hand, he adopts the plan of hereditary sover- 
eignty, he will deal with few families at a time ; and while, if 
they are extremely well-bred to begin with, a large proportion 
will be exceptional, yet a glance at the upper lines of this table 
will be enough to indicate that he will be confronted by a good 
many hereditary rulers who are far from exceptional (see espe- 
cially row e). He has taken a useless hazard, and this is the 
inevitable handicap of an hereditary monarchy. From the stand- 
point of evolution the principle is wrong. 

The above ought to make it clear why the breeder and the 
politician should adopt opposite methods. If service alone is 
wanted, it is better to find it than to breed it ; and that is why 
it is often better to buy a particular type of animal than to 
attempt to produce it, especially if the type is at all unusual, as 
in the case of the " fire horse." 

SECTION XI — FRATERNAL VARIABILITY, — OFFSPRING 
OF SAME PARENTS NOT IDENTICAL 

The offspring of like parents are not only unlike, but the suc- 
cessive offspring of the same parents vary widely. The only 
data compiled on this important fact are contained in the table 
on the following page, from Galton's studies in stature. 

This table presents all the characteristics of the ordinary 
regression table but in a degree slightly less pronounced. This 
shows that the same laws of regression and progression apply 
zvitJiin the family as apply bettveen families. 

Alluding to this significant fact, Galton remarks : ^ 

It appears that there is no direct hereditary relation between the personal 
parents and the personal child, except perhaps through little-known chan- 
nels of secondary importance, but that the main line of hereditary connec- 
tion unites the sets of elements out of which the personal parents had been 
evolved with the set out of which the personal child was evolved. . . . 
This is why it is so important in hereditary inquiry to deal yN\i\\ fraternities 

1 Galton, Natural Inheritance, pp. 19-20. Italics are mine. 



HEREDITY 



501 



vO 


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502 TRANSMISSiaN 

rat/ier than with individuals^ and with large fraternities ratlier tlian with 
small ones. We ought, for example, to compare the group containing both 
parents and all the uncles and aunts with that containing all the children. 

Here is the very gist of the whole matter, showing the folly 
of dealing with individuals in questions of breeding. All the best 
evidence shows that selection based upon the individual, without 
regard to the group to which he belongs, will never result in 
concentration of excellence. It is only by persistent selection, 
based on the groups as a whole (purity of pedigree in the sense 
of uniformity of type), that we shall ever free even the family 
from the drag of the race, and make real progress in improvement. 

Harold and Miss Russel, the sire and dam of Maud S., were 
owned at Woodburn for many years, but of all their get only one, 
Maud S., developed high speed. Why } The question cannot be 
answered any further than it can be inferred from the principle 
just stated and from the well-known methods of cleavage of the 
nucleus in cell division and in maturation ; but with these facts 
in mind, we should hardly expect that tivo identical individuals 
zvould ever arise, even frovi the same parents. 

The earlier offspring live longer than do the younger children 
of the same parents. Having established the fact that successive 
offspring of the same parents are different, there remains the 
task of determining to what extent this fraternal variability is 
heterogeneous, and to what extent it may be correlated with age 
or with some similar circumstance that tends to throw the off- 
spring into a regularly graded series of some sort. 

On this point we know but little. To the eye this variability 
appears quite heterogeneous, but studies in longevity, for ex- 
ample, have fully established the fact that in man the older chil- 
dren, on the average, live longer — that is, have longer lives — 
than do the younger ones of the same family. This difference, 
as between the oldest and the youngest, amounts to no less than 
four years. ^ Whether the same or a similar decline takes place 
in other characters and faculties only exhaustive studies could 
determine. There is no reason to doubt that general principles 
apply equally to man and to other animals, excepting in so far 

1 See article on " Inheritance of the Duration of Life," by Beeton and Pearson, 
Bionietriha, Vol. I, Part I, pp. 50-76. 



HEREDITY 



503 



as social and other somewhat artificial conditions of life may 
intervene, and we shall anxiously await the results of further 
investigation into the character and range of difference between 
offspring of the same parents. 

Individuality. Whatever the results of investigation in this 
direction, and whatever gradual advance or decline may be 
established among the members of the same family on the aver- 
age, the fact remains that variability is largely heterogeneous as 
between individuals , and that a marked individuality pervades 
all offspring, either of the same or of different parents. 

This lessened deviation between members of the same family 
as compared with descendants in general is due to the fact that, 
among brothers, not only both immediate parents but all ances- 
tors are identical. The differences that do exist within the same 
family serve to show the wide divergencies possible with the same 
hereditary elements, although, in studying adults, some allow- 
ances must always be made for differences in development due 
to external causes. While members of the same family are in gen- 
eral reared more nearly alike than are members of different fam- 
ilies, yet in a large sense every individual has a life history of his 
own quite distinct and in many senses different from that of any 
other individual of his own or of any other generation. Now this 
life history affects development and accounts for some of the 
differences between adult individuals. Not all of the variability 
within a family can, therefore, be assigned to hereditary influ- 
ences, but that a large share of it is due to such influences is 
rendered extremely likely by the well-known fact that successive 
ova, spermatozoa, or pollen grains from the same individuals 
are not alike either in their genesis or in their behavior after- 
ward. The very mechanism of maturation strongly suggests 
profound qualitative differences, and tends to modify our as- 
sumption that all children of the same parents possess identical 
hereditary elements. The experience of breeders everywhere is 
that offspring of the same individuals are not slightly different 
but in general they are widely different. Whether, and to what 
extent, these differences can be lessened by selection and by 
relative purity of ancestral gametes are questions on which light 
is sorely needed. 



504 TRANSMISSION 

SECTION XII — CHARACTERS TEND TO COMBINE IN 
DEFINITE MATHEMATICAL PROPORTIONS ^ 

The student working with large populations must be struck 
by the remarkable similarity of the general features of all fre- 
quency distributions and arrays. Broadly interpreted, this sug- 
gests a strong mathematical basis in reproduction. 

In all forms of life halving and doubling are basic processes. 
The number " two," therefore, as a mathematical conception, lies 
at the bottom of a large share of our biological problems, espe- 
cially those of variability, and a little consideration will show 
that the usual form of the frequency distribution is the natural 
result of the reproductive processes, — indeed, that the facts of 
variability largely^ though not exclusively, follow the ordinary 
mathematical laws of combinations and probabilities. 

The mixing of pure forms. To illustrate this fundamental fact 
let us undertake to follow the history of two characters brought 
together for the first time, and the manner in which they will 
naturally appear in the offspring. 

To put the matter in its simplest form, let us suppose a herd 
of pure blacks to meet and mingle with a herd (of equal numbers) 
of pure reds, and that they breed together without restraint, — that 
is, without selection. They will then mate indiscriminately ; that 
is to say, a black female will mate indifferently with a black or 
a red male, — sometimes with one and sometimes with the other. 

This being true, one half the offspring of the black females 
will be pure black (designated by B'^) and one half will be mixed, 
black and red (designated by BR). 

The same principle applies to the red females, whose progeny 
will, in like manner, be equally divided between the mixed off- 
spring and Xh^ pure reds. 

Expressed in tabular form we should then have : 

For every 200 offspring of black females 100 ^^ + 100 BR 

For every 200 offspring of red females 100 BR -\- 100 R^ 

Total distribution, 400 offspring 100 ^^ + 200 BR + \oo R^ 

In proportion of B" + 2 BR + R" 

1 This principle was first announced by Quetelet, 1S46, in Lettres sur la theorie 
des probabilites. See Vernon, Variation in Animals and Plants, p. 12. 



HEREDITY 



505 



It is evident that, whatever the numbers involved, the above 
is the p7'oportion in which the pure and the mixed forms will 
naturally appear in the first generation of admixture between 
two pure forms. 

From this we see that indiscriminate breeding of distinct 
characters results in both "pure" and "crossed," or mixed, 
forms in their descendants, and this in the proportion of 1:2: i. 
Now this is a short "frequency distribution," in which the 
middle term represents the individuals of mixed breeding and is 
equal to the sum of the two extremes. 

The second generation, or second remove from pure forms. 
What now will be the character of the next generation, as bred 
from the individuals B'^ (pure black), BR and BR (mixed), and 
^ (pure red) .? 

Continuing the assumption of indiscriminate mating and uni- 
form fertility, we shall have the following, remembering what 
are the relative numbers involved, and that in tJie long run every 
kind of female zvill mate with every kind of male, producing 
offspring of the following character : 

Character of Offspring produced by Females of Different Kinds 

WHEN MATING WITH MaLES OF DIFFERENT KiNDS WITHOUT SELECTION 



Females of Different Kinds in theik 


Different Kinds of Sires in their 
Relative Frequency 


Relative Frequency 


R^ 


2 BR 


R^ 


Offspring of B^ mating with 

Offspring of 2 BR mating with .... 
Offspring of R' mating with 


B^ 

2.B^R 
B^R-^ 


2B^R 
4 B-^R^ 
2 BR^ 


B^R^ 
2BR^ 
A'* 


Total 


B^ + 4 B^R + 6 B^R^ + 4 BR^ + R^ 



This, then, expressed in its simplest form and the lowest 
terms, is the population resulting from two generations of indis- 
criminate breeding between forms originally pure. 

Two things are noticeable about this total. First, it has all 
the characteristics of the ordinary frequency distribution (i, 
4, 6, 4, i) ; and, second, it is a complete expression of the 



5o6 



TRANSMISSION 



binomial B -V R expanded to the fourth power according to the 
binomial theorem. 

Succeeding populations follow the law of the binomial theorem 
except as interrupted by selection or differences in fertility. In 

the breeding of this third generation inter sc we find the numbers 
becoming rapidly complicated, but from the fact that it always 
follows the binomial theorem we can write the normal distribu- 
tion for the fourth generation of descendants of any pair of 
characters as follows : ^ 

{B ^ Kf = B^ ^'^ B'R + 28 B^R" + 56 B^'R^ 

+ 70 B^R^ + 56 B^R'' + 28 B^R'' + 8 BR'' + 8 R\ 

Analyzing this "fourth-generation population," we find : 

1. That no less than nine color combinations are represented, 
ranging all the way from pure black to pure red. 

2. That the frequency numbers representing the various com- 
binations, I, 8, 28, 56, 70, 56, 28, 8, I, form a symmetrical fre- 
quency distribution whose total is 256, only two individuals of 
which are pure. 

3. That future breedings would become rapidly complicated, 
but that we should always have one pure black and one pure 
red, with all possible combinations betzveen the two. 

4. That the actual color combination of the individual cannot 
in most cases be inferred from appearances. For example, there 
is but one real black and but one real red in the whole popula- 
tion. However, the 28 I^I^ will look like blacks, because there 
have been six infusions of black to but two of red, while the 
reverse is true of another equal number, 28 B'^R^. The 70 B^R^, 
which is the largest number of all, constituting nearly one third 
of the entire population, is equally balanced as to color tenden- 
cies, but will appear to be of the color that is most noticeable, 
— in this case probably a dark red. 

Combinations of three characters. Though the numbers become 
more rapidly complicated, the same principles apply when deal- 
ing with three or more characters. For example, suppose we 
introduce a third color, white. We shall then have as the result 
of the first mating the following : 

1 The student can easily verify these figures by the plan already outlined. 



HEREDITY 



507 





Males 




B 


R 


w 


Offspring, female B 

Offspring, female R 

Offspring, female IV 


BR 

BIV 


BR 

R2 

RIV 


BW 

RW 
IV2 


Total 


B-^ + 2BR -{■ R^+2B IV+ 2 R IV + IV^ 



Here we have, after one indiscriminate mating all around, a 
total of nine animals, of which one is pure black, one pure red, 
and one pure white, with the other six divided into three 
groups, each of two colors combined, — that is, all the pos- 
sible combinations. 

If now this generation be bred into, itself, new and strange 
combinations are inevitable, giving rise to a complicated popula- 
tion, as follows : 

Table of Offspring showing the Fourth Generation in the 
Attempt to combine Three Characters 



Dams 


Sires of Same Breeding as Dams 


B-^ 


2 BR 


R-^ 


2 Bll- 


2 II'R 


;/-2 


B-^ 
2 BR 

R^ 
zBJV 
2 RIV 


B^ 
2B^R 

B-^R^ 
zB^JV 
2 B'^R IV 

B2ir2 


2B-^R 
4 B-^R-^ 
2 BR"^ 
\B^RW 

abr^w 

2BRIV^ 


B-^R^ 
2 BR^ 

R^ 
2BR^W 
zR^W 

R^IV^ 


2 B^ IV 
4B-^RIV 
2 BR^ IV 
4 B"- IV^ 
4 BR IV^ 
2 B IV» 


2B-^RIV 
4 BR^ IV 
2 A'3 IV 
4BRW^ 
4R^IV2 
2RIV^ 


2BRIV^ 

R^ W^ 
2BIVS 
2 R /F3 
IV* 



B* + 4 B'^R + 6 B^R^ + 4 B^IV+ 12 B^RIV+ 6B^IV^ + 4 BR^ + 12 BR'^IV 
+ 12 BRIV^ + R* + 4 R^IV+ 6 R^IV^ + 4 B IV^ + 4 RW^ -\- ^F*, — total, 81 



Here are eighty-one individuals of no less than fifteen differ- 
ent color combinations, all effected within two generations from 
purity. Out of the eighty-one individuals, three, and three only, 
are as pure as if no admixture had been attempted, suggesting 
that a certain small proportion ivill always remain unmixed in 
Jieterogeneous breeding, no matter how lojig continued. 



5o8 TRANSMISSION 

All the rest are mixed in color, no matter what their appear- 
ance. Of these the 4 B'^R and the 4 B^W will most likely 
appear black, as will also, in all probability, the 12 B'^RJV, 
because the B elements are clearly in the majority. Similarly, 
equal numbers will appear red, and other equal numbers will 
seem to be white, — unless both colors appear, as in roans and 
piebalds. 

There are three sets of six each (6 B^R"^, 6 B^JV^, and 
6R'^IV'^) in which but two color elements are present, but in 
which the appearance will probably be fixed by the color that is 
most pronounced and which, therefore, tends to dominate the 
other; thus the 6 B'^R^^ will appear as black or very dark red. 

Thus it is that appearances are often deceiving, and that 
which looks like a heterogeneous jumble is, after all, an orderly 
collection of mathematically exact combinations. A scheme like 
the above serves to show the exceedingly complicated, yet 
orderly, systems that necessarily arise in bisexual reproduction, 
whatever the characters involved, — complexity that increases 
rapidly, indeed almost inconceivably, as generations multiply. 

Because of these facts reproduction would be reduced to a 
problem in probabilities, and we should have all possible combi- 
nations presented, were it not for the fact that selection is 
always at work to eliminate certain unfavored forms, and that 
differences in fertility serve to give certain combinations still 
further advantage over others. However, we are not to over- 
look the fact that, even though certain values be withdrawn 
from such a distribution, the laws of probability continue to ap- 
ply to the remaining values, whose combinations will take place 
as before, and in the end give rise to a distribution not very 
different in form from that which would have arisen if no 
values had been removed. 

An ultimate confirmation of this statement is found in the 
fact that . most frcqitency distributions are fairly symmetrical, 
and that one large enough to be fairly ^'smooth,'' tvJiatever the 
number of its terms or the size of its frequencies, can be closely 
reproduced by expanding a binomial. If the distribution be 
symmetrical, the terms of the binomial should be numerically 
equal {B + 7?, or ^ + i) ; but if its mode is not near the middle 



HEREDITY 509 

but nearer one extreme, then the terms of the binomial should 
be numerically unequal ^ {B + 2 R \ |^ + | ; etc.), — a case which 
would fit our illustration had the number of R females been 
twice the number of B females. 

The ease with which all distributions can be fairly well 
" fitted " shows beyond a doubt that, even with selection and 
infertility at work, the final result is largely such as would arise 
from independent probability, — a fact which goes to show that 
problems in heredity are essentially statistical problems. 

The hopeless tangle in which characters soon become involved 
through bisexual reproduction shows the utter futility of 
attempting to infer anything whatever from individuals, and 
the almost mathematical certainty of being able to detect 
almost any principle or law of descent by careful study of 
entire populations. 

1 For the convenience of the student the formula for expanding a binomial 
to any power is given here. It is 

{A + BY = A- + nA'-^B + " ^'^ ~ '^ A"-^B^ + -(--^)("-^~) ^«-3^3 

1-2 I ^-S 

+ "(''-')("-'-)<"- ^^^A"-^B*+ +.AB"-^ + B". 
I •2-3-4 

This formula gives 

{A + Bf = A-2 + 2AB + B- 
\a + Bf = A-i + 2 A^B + 3 AB^ + B^ 
\a + B)^ = .-t/4 + 4 A^B + 6 A'^B-^ + 4 AB^ + B* 

Ia + Bf = A^ + 6 A^B + 1 5 A^B^ + 20 A^B^ + 15 A'^B^ + 6 AB^ + B^ 
\a + Bf = A^ + ?, A'^B + 28 A'^B^ + 56 A^B^ + 70 A^B^ + 56 A^B^ 
+ 28^2^96 + 8^.5^ ^ B^ 

Thus in all cases the coefficients form a series like a symmetrical frequency 
distribution. If, however, the second term be taken as 2B, then the coefficients 
will be substantially altered, forming a skew. 

Karl Pearson has well established the fact that frequency distributions obtained 
experimentally can often be fitted better by the terms of the binomial {A + BY 
when 11 is not restricted to be a positive integer. In this case the expansion does 
not terminate, but takes the general form 

(^ + BY = A" + .A"-^B + !iiii— L> A"-^-B^ + "("-')("-^-) A"-W^ + • • • 

12 i-2-j 

to infinity, in which the general, or rth, term is 

n{7i - i){u - 2) • ■ (» - r + 2) ^„_2 + i^,._i 
I .2. 3- ••(;-- I) 



5IO TRANSMISSION 

Distinctions between inheritance and development. There is 
still another reason why the true nature of an individual cannot 
always be detected by appearances, and this is found in the 
relative development of inherited characters. 

For example, suppose that in the illustration given on page 
506 B and R represent size instead of color. If B represents 
great size and R extreme smallness, then, by all the principles 
of inheritance, the 28 B^R"^ of the scheme previously discussed 
are born for something above the mean size, which would be 
represented by the 70 B^R^. 

Suppose, however, that through insufficient feed many of 
these individuals fail to develop the full size which is their birth- 
right. Such individuals then appear small, like the B'^R^, or 
perhaps even the R'^. 

So it comes about that these twenty-eight individuals, though 
born alike as to tendencies with respect to size, and each repre- 
sented by formula B^R"^, are yet very different when examined 
after development, which of necessity depends upon the condi- 
tions of life. And so it is that, owing to differences in develop- 
ment, relative quality as we infer it from the appearance of the 
adult is but a rough and often misleading indication of the char- 
acters actually present through inheritance. Relative strength 
of characters as inherited may be known with certainty only 
through an intimate knowledge of pedigrees. Thus a buyer of 
an adult animal would have great difficulty in selecting, from 
appearances only, the individual born with greatest tendency to 
develop unusual size. 

The mathematical nature of descent not due entirely to bisexual 
reproduction. The truth of this statement we deduce from the 
fact that offspring asexually produced vary on the same plan as 
do individuals that are bisexually produced. It is to be inferred 
also from the further fact, already alluded to, that successive 
ojf spring of the same parents are not alike, but form a distribution 
of the same general outlines as that of the total population. 

This shows that the mathematical element in reproduction is 
to be sought not only in bisexual union, but farther back also 
in the facts of cell division and the splitting of the chromosomes, 
— if not indeed in their very constitution. 



HEREDITY 



511 



What is it that is transmitted? Evolutionary literature abounds 
in such terms as "tendencies," "reversion," "ancestral bias," 
and many others which imply an intangible something back of 
the immediate parent. The common impression of transmission 
is of something "handed down," or passed on from one genera- 
tion to the next, and that the visible characters represent the 
inheritance. It is evident, however, that that which is trans- 
mitted is not the character, but rather the elements out of which 
the character is built up, and that these elements are capable of 
many and varied combinations. 

What these elements may be like, and what the ultimate units 
of variability may be, — whether chromosomes or some infinitely 
smaller component, — we do not know. Physiological units have 
not been discovered, but the, laws under which they combine to 
form characters, and under which the characters combine to form 
individuals within racial limits, — these have been sufficiently 
studied to warrant the assumption that they follow essentially 
the ordinary mathematical principles of permutations and com- 
binations working under the laws of probability. ^ In other words, 

1 By "combinations" is meant the number of different groupings that can be 
made from a given number of objects without regard to the arrangement of the 
members. Thus, with a, b, c, d, taken three at a time, we may have four com- 
binations, namely, abc, abd, acd, bed ; or, taken two at a time, we have si.x com- 
binations, namely, ab, ac, ad, be, bd, cd. Each of these combinations may have 
two or more permutations, depending upon the orde?- in which the numbers 
stand; thus, the combination abc is capable of the permutations abc, acb, bac, bca, 
cab, cba. 

The number of combinations possible with a given number of units depends 
upon the number taken in each grouping. 

The general formula is 

_ ■"(« - i) ■ • ■ (n - r + i) 
I • 2 • 3 • • . ;- 

in which ;; is the total numl^er and r is the number in each group. 

The number of permutations, or different arrangements, possible also depends 
upon the number in each group. The number of permutations of objects taken 
two at a time is Ji(n — i) ; taken three at a time it is ;/(;/ — i) {>' — 2), and so 
on; taken r at atime it is therefore n{n — \) [n ~ 2) . . . (// — ;■ + i). 

When all the numbers enter into each permutation, then the formula amounts 
to the multiplication together of all the natural numbers, from unity up to the 
number itself; that is, the number of permutations of five letters, a, b, c, d, e, is 
equal to i x 2 X 3 X 4 X 5 = 1 20. 

To give an illustration of the probability of an event, if a penny be tossed the 
odds are even that heads will be up, because there is but one alternative. This 



512 



TRANSMISSION 



it is the elements of racial characters that are transmitted, and 
out of these elements all possible combinations arise. Some 
combinations are unsuited to the conditions of life and others 
are relatively or absolutely infertile, making blank spots in the 
system which otherwise would be mathematically complete and 
substantially regular. 

Even with these omissions, however, the distributions into 
which characters fall lend themselves to ordinary mathematical 
methods of study, giving the strongest ground for the confident 
belief that the laws of heredity will not long continue to be 
regarded as unexplained mysteries, subject to all sorts of 
exceptions and reversions, but that characters in descent will 
be found to observe as well-defined and well-known mathematical 
principles as do chemical elements in their similar but vastly 



probability we express as -J. On the other hand, if a dice be thrown, the chance 
of any particular side coining up is but |, for there are six possibilities. If a 
wager be laid that the number 3 comes up, the odds will be five to one against it, 
for its chances are one out of six. If two dice are thrown, the chance of a 3 
coming up on each at the same time is ^ X ^, or ^^^ ; but the chance of two 
different numbers, as 3 and 4, coming up together is doubled. This is because 
the chance of one dice turning up either a 3 or a 4 is not \, but \ ; after which the 
second dice must supply the proper mate, whose chance is but \, and i x ^ = yj. 

This means that in the long run this event will happen once for every eighteen 
throws, though it cannot be confidently predicted that it will happen on the 
eighteenth, the thirty-sixth, or on any other particular throw. 

The word "chemistry" has nine different letters. By the principle of permu- 
tations just laid down, these nine letters are capable of 1x2x3x4x5x6 
X 7 X 8 X 9, or 362,880, different arrangements, only one of which will spell the 
word " chemistry." If, therefore, the letters of this word should be tossed into the 
air and left to fall into a groove and arrange themselves in line by chance, 
the odds would be 362,879 to i against the letters taking the proper arrangement 
to spell the word; but if the tossing should be continued, it is certain that in 
the long run they would fall into the proper order to spell this particular word. 
Sooner or later, therefore, if the chance differs from zero, the event is sure to 
happen ; and for this reason nothing is more certain than chance, if only a 
sufficient number of possibilities be afforded. 

The mind is lost in the presence of large numbers, and the judgment is con- 
fused when the improbable happens, yet that these letters would ultimately spell 
this word by pure chance is an event certain to take place ; not only is this so, 
but /;/ the long run it will happen once for every 362,880 throws made. 

A little careful study of the possible combinations, even of a few elements, 
and of the certain occurrence of possible, even though improbable, events, will 
lead the student to work with variables in large numbers with greatly increased 
confidence. 



HEREDITY 



513 



simpler combinations. This is only another way of expressing 
the conviction that before many years — if the present activity 
in statistical studies continues — the laws of descent will be more 
accurately known than any other phase of biological science. 
While the individual will alwa}s be an uncertain article, as is 
bound to be the case where the element of chance is involved, 
yet this same chance, under the doctrine of probability, becomes 
one of the best known and most dependable principles where 
sufficiently large numbers are concerned. Because of this, the 
uncertainty as to individuals gives way to the most definite 
knowledge as to populations, all of which leads to the inevitable 
conclusion that the systematic study of groups of individuals is 
the only reliable way to study heredity, and the only method 
likely to afford data from which we may safely draw conclusions 
as to laws of descent. 

SECTION XIII — MENDEL'S LAW OF HYBRIDS 

Mendel's law, as it is called from its original discoverer,^ 
arises naturally from the principle outlined in the last section, 
namely, that characters te^d to combine in definite proportions, 
so that the natural offspring resulting from the mating of two 
lines of parents with different characters, B and R^ is of the 
general form B'^ + 2 BR -\- R^. Mendel's law has special refer- 
ence to the apparently crossed portion of the population {BR), 

1 Gregor Johann Mendel, an Austrian monk, and abbot of Briinn, was born 
in 1822 and died in 1S84. He carried out his breeding experiments — mostly 
with peas — in the garden of his cloister, publishing the results in the form of a 
few brief papers in an obscure journal in Briinn, 1853-1S65. Partly from the 
obscurity of the journal, but more from the fact that scientists were interested in 
totally different lines of study, these papers were practically lost to the scientific 
world for more than thirty years. Upon the appearance of De Vries' paper announc- 
ing the rediscovery and confirmation of Mendel's law and its extension to a great 
number of cases, two other observers came forward almost simultaneously, and 
independently described series of experiments fully confirming Mendel's work. 
Of these papers the first is that of Correns (1900), who repeated Mendel's 
original experiments with peas having seed of different colors. The second is a 
long and very valuable memoir of Tschermak, which gives an account of elaborate 
researches into the results of crossing a number of varieties of Pistim sativiivi 
(see Mendel's Principles of Heredity, by Bateson, p. 14). The latter experimenter 
worked mostly on peas ; Correns, on peas and corn (maize) ; while De Vries 
worked with many species and a great variety of characters. 



514 TRANSMISSION 

and it aims to predict the character of the offspring when these 
hybrids are bred together. 

How will this hybrid breed ? Will it continue " pure," or 
will it break up into its component parts ? This question 
Mendel's law attempts to answer, and the essence of the law 
can be stated in two propositions : 

1. When crossed forms, or hybrids {BR), are bred together, 
their offspring will not all resemble the crossed parents, but one 
fourth, or 25 per cent, will be like the original pure parent B, 
another fourth will be like the other original pure parent R, and 
one half, or 50 per cent, will resemble the crossed forms, so 
that the offspring of the cross will tend to assume the original 
general form of B^ + 2 BR + R'^. Of these the "pure" indi- 
viduals will breed as true as to the cJiaractcr m question as if 
their ancestors had never been subjected to crossing ; and the 
50 per cent of crosses, when bred among themselves, will again 
split up into pure and crossed forms in the proportion of i : 2 : i, 
so that BR bred with BR will give offspring represented by 
B"^ + 2 BR^ + R^ indefinitely. In other words, the offspring of 
hybrids will not all be hybrids, but they will assume the same 
general proportions that are assumed when pure forms are 
allowed to breed together indiscriminately. 

If this theory be true, it shows the impossibility of breeding 
a cross true to its own type, on account of its innate tendency to 
split up into its original pure or uncrossed forms, — a tendency 
which has long since been encountered by breeders ambitious 
to fix a fortunate cross, and which has gone far to convince the 
popular mind of the difficulty in effecting a real cross. 

2. The second fundamental in Mendel's law is the distinction 
between dominant and recessive characters. If the characters 
in question were evenly "balanced," and equally discernible, 
then in a population like 75^+2 BR + R^ the B''- would be 
clearly defined, say black. The F& would also be clearly defined, 
say red, and the 2 BR would be some kind of blend or mixture 
of the two ; in other words, such a population would be easily 
assorted into three groups in the proportion of 1:2:1. 

On the other hand, suppose one character to be strong and 
easily noted, as a red color, or a strong, heavy stem, while the 



HEREDITY 5 i 5 

other is extremely delicate, as a light shade of blue, easily lost 
in the red, or a lightness of foliage, easily obscured by a 
heavy stem.^ Now, under circumstances such as these, the less 
noticeable, or " recessive," characters will be visible only in the 
individuals that are pure reeessives, all others being dominated by 
the more pronounced eharaeter. Thus, if D stands for dominant 
(red petal or strong stem) and r for recessive (light-blue petal 
or delicate foliage), then the actual distribution would be D'^ -V 
2 Z>/'+ r^ as before ; but in this distribution three out of four 
individuals would be distinguished by the dominant character, 
while the less assertive, the recessive character, would be ob- 
scured except in the 25 per cent in which it exists unmixed 
with the dominant. Hence an individual showing a recessive 
character may be known at once to be pure, but we cannot 
tell by looking at individuals showing the dominant character, 
which are pure and which are mixed. We know, in fact, that 
we have both forms in the proportion of i to 2, but in a case 
of this kind 75 per cent would appear Xo be dominant, while only 
25 per cent would appear to be recessives. In reality, 25 per 
cent -AXQ pure dominants, the other 50 per cent being apparently 
dominants, but actually mixed, — a fact that immediately be- 
comes evident when they are bred among themselves, as they 
at once give rise to the characteristic distribution, with the 
proper 25 percent of pure recessives. 

Inasmuch as few pairs of characters are equally balanced and 
equally able to make themselves evident, it is generally true 
that any generation from crossed parentage will show 75 per 
cent dominant (really 25 pure and 50 mixed) and 25 per cent 
recessive, instead of the typical 25, 50, and 25 that would 
appear if the characters were equally evident and equally 
assertive. 

Distinction between characters and individuals. The reader 
will be misled if he takes individuals into consideration here 
instead of characters. The entire discussion applies to charac- 
ters taken singly, and when we say of an individual arising from 
hybrid parents that he will " breed pure," we mean only as to 

1 It is clear that only characters that are " mutually exclusive " can be used in 
experimenting on or illustrating this subject. 



5 1 6 TRANSMISSION 

the single character in question ; for example, hybrids of Jerseys 
and Shorthorns would not breed pure individuals oi either breed, 
though pure Jersey and pure Shorthorn characters would appear 
freely. 

If we are to consider many characters at once, we may easily 
satisfy ourselves as to the chances of an absolutely pure ijidi- 
vidual arising out of a hybrid ancestry. 

If one fourth of the population arising from a hybrid ancestry 
can be said to be pure as to a single character, the question 
arises as to what proportion of this number can be considered 
as " pure " with respect to tivo characters. 

From the fact that this second character enjoys the same 
chances as to purity as did the first, we conclude that one fourth 
of the number, or one sixteenth of the whole (| X ^), will be 
pure as to two characters. By the same reasoning we know that 
I X I X I carried to any number of terms will express the chance 
of an individual being pure with respect to the corresponding 
number of characters. If many characters are involved, there- 
fore, the chances of a pure individual arising out of mixed 
breeding are exceedingly slight, and our chance of being able to 
" pick him out " by his appearance is still more remote. 

Experimental evidence.* It remains now to inquire somewhat 
carefully into the evidence upon which these propositions are 
founded. 

Mendel's first experiments were conducted with garden peas, 
and covered the following characters : ^ 

1. Differences in fonn of ripe seeds, — either round and 
smooth or with shallow wrinkles, or else angular and deeply 
wrinkled. 

2. Differences in the color of seed albumen (endosperm) — 
either pale yellow, bright yellow, orange, or green. 

3. Differences in the color of the seed coat, — white, gray, 
gray brown, leather brown with or without violet spotting. 

4. Differences in form of ripe pod, — whether inflated or 
constricted between seeds. 

1 For a translation of Mendel's original report, see Bateson, Mendel's Prin- 
ciples of Heredity, pp. 40-103, from which are taken the data herein given. 
- Ibid. pp. 45-46. 



HEREDITY 5 i 7 

5. Differences in coloi- of unripe pods^ — light green, dark 
green, or vividly yellow. 

6. Differences in position of Jfozvers, — whether axial or 
terminal ; that is, whether distributed along the main stem or 
bunched at the top in a "false umbel." 

7. Differences in leiigth of the stem, — varying from 9 inches 
to 6 or 7 feet. 

It is perfectly easy to see that many of these characters would 
be doininant over others, the less noticeable being "lost" to 
view in the hybrid forms. For example, dark green would be 
dominant over light green and over most shades of yellow ; long 
stems over short ones ; and dark colors generally over light ones. 

The preponderance of the dominant character over the reces- 
sive is so pronounced as to lead Mendel to remark that fre- 
quently " one of the parental characters was so preponderant 
that it was difficult or quite impossible to detect the other in 
the hybrid." In each of the seven crosses of peas, he adds, 
" The hybrid character resembles that of one of the parent 
forms so closely that the other either escapes observation com- 
pletely or cannot be detected with certainty." ^ Of the charac- 
ters used, the following were found to be dominant : ^ 

1. The round or roundish form of seed. 

2. The yellow coloring of the endosperm. 

3. The gray, gray-brown, or leather-brown color in the seed 
coat. 

4. The inflated over the constricted pod. 

5. The green color in the unripe pod. 

6. The distribution of flowers along the stem. 

7. The greater length of stem. In respect to this point the 
investigator remarks that stems i foot long crossed with stems 
6 feet long gave rise to stems from 6 feet to 7I- feet long. 

The first, or hybrid, generation. Because of the overpowering 
influence of the dominant characters, the " hybrid," or cross, 
could not commonly be distinguished from the " pure " parent 
possessing the dominant character. This agrees with the experi- 
ence of breeders generally. 

1 Bateson, Mendel's Principles of Heredity, p. 49. 

2 Ibid. p. 50. 



5i8 



TRANSMISSION 



The second generation, bred from hybrids. When, however, 
these hybrids were bred among themselves, the recessive charac- 
ters came into evidence, constituting in all cases approximately 
one fourth of tJie offspring, leaving the other 75 per cent to be 
apparently dominant, — actually, 25 per cent pure dominant and 
50 per cent apparently dominant but really mixed. 

Thus, in Experiment i (as to form of seed), from 253 hybrids 
7324 seeds were obtained in the second trial year. Among them 
5474 were round or roundish and 1850 were angular, —a ratio 
of 2.96 to I. 

In Experiment 2 (as to color of endosperm), 258 crossed 
plants yielded 6022 yellow and 2001 green, — a ratio of 3.01 
to I. 

Distribution of characters. In each of these experiments botJi 
kinds of seed were usually found in the same pod, showing that 
the ovule, and not the pod, is the unit. Not only was that the 
case, but the proportion of three dominants to one recessive 
held only in the long run, and did not hold for individual plants, 
as is seen in the following table giving the classification of the 
offspring of the first ten plants in each experiment.^ 









Experiment No. 2, Color of 


Plants 


Experiment No. 


I, PoRM OF Seed 


Endosperm 




Round 


Angular 


Yellow 


Green 


I 


45 


12 


25 


II 


2 


27 


8 


32 


7 


3 


24 


7 


14 


5 


4 


19 


10 


70 


27 


5 


32 


II 


24 


13 


6 


26 


6 


20 


6 


7 


88 


24 


32 


13 


8 


22 


10 


44 


9 


9 


28 


6 


50 


14 


10 


25 


7 


44 


18 



From this it appears that the dominant always exceeds the 
recessive in number, but that the proportion of 3 to i is 

^ Bateson, Mendel's I'rinciples of Heredity, p. 53. 



HEREDITY 



519 



not maintained in each individual plant. As to whether this 
comes from difficulties in identifying and classifying doubtful 
specimens, or from some biological reason, Mendel does not 
express an opinion, though the point is important. 

In other experiments the ratio between the dominants and 
the recessives was in all cases approximately 3 to i. In Experi- 
ment 3 (as to color of seed coats), it w^as 3.15 to i ; in Experi- 
ment 4 (as to form of pods), it was 2.95 to i ; in Experiment 5 
(as to color of unripe pods), it was 2.82 to i ; in Experiment 

6 (as to position of flowers), it was 3. 14 to i ; and in Experiment 

7 (as to length of stem), it was 2.84 to i, but the numbers were 
relatively small (787 and 277) as compared with the numbers 
involved in Experiments i and 2. 

The third generation, — second from hybrids. According to 
Mendel,^ " those forms which in the first generation maintain 
the recessive character do not further vary in the second genera- 
tion as regards this character ; they remain constant in their 
offspring. 

" It is otherwise with those which possess the dominant 
character in the first generation (bred from hybrids).^ Of 
these, two thirds yield offspring which display the dominant and 
recessive characters in the proportion of 3 to i, and thereby 
show exactly the same ratio as the hybrid forms, while only one 
third remains with the dominant character constant." That is 
to say, of the 75 per cent rr//^r;r;if/' dominants, one third, or 25 per 
cent, of the whole breeds pure dominants, showing that this 
proportion is actually what it appears to be, namely, pure domi- 
nants, while tivo thirds, or 50 per cent of the whole, yield both 
dominants and recessives in proportion of 3 to i, showing their 
essentially hybrid or crossed nature, and that their dominance 
is apparent rather than actual. The separate experiments yielded 
ratios as follows : ^ 

In Experiment i, among 565 plants raised from round seed 
193 yielded round seeds only, and remained therefore constant 
in this character, while 372 gave both round and angular seeds in 

1 Bateson, Mendel's Principles of Heredity, p. 55. 

2 That is, with the 75 per cent apparently dominant. 

3 Bateson, Mendel's Principles of Heredity, pp. 55-58. 



520 



TRANSMISSION 



the proportion of 3 to i . The number of the hybrids as compared 
with the constants was therefore 1.93 to i. In Experiment 2 it 
was 2.13 to I ; in Experiments 3-7 the numbers were small, but 
approximated the same ratio. 

From this Mendel states the following conclusion regarding 
the offspring of hybrids ^ (italics his) : 

// /s 7101U clear iJiat the Jiybrids form seeds having one or other of the two 
differentiating characters^ and of these one half develop again the hybrid 
forjn, while the other half yield plants which remain constant and receive 
the dominant or recessive characters {^respectively^ in equal numbers. 

This conclusion, which seems to be in accord with his results, 
is clearly against the possibility of effecting a real cross between 
characters that behave as do those in question. 

Subsequent generations. On this point Mendel says : ^ 

The proportion in which the descendants of the hybrids develop and split 
up in the tirst and second generations presumably holds good for all subse- 
quent generations. Experiments i and 2 have already been carried through 
six generations, 3 and 7 through five, and 4, 5, and 6 through four . . . 
and no departure from the rule has been perceptible. The offspring of the 
hybrids separated in each generation, in the ratio of 2 : i : i, into hybrids 
and constant forms. 

That is to say, of the offspring of hybrids one fourth resembled 
one pure parent and ever afterward bred true with respect to the 
character in question ; one fourth resembled the other and also 
bred true ; and one half still remained hybrid, but its offspring, 
in its turn, fell apart after the same ratio i : 2 : i. 

When more than two characters are involved. Mendel con- 
ducted investigations with plants differing in a number of char- 
acters simultaneously and concludes as follows : "^ 

That the offspri/ig of the hybrids in which se7>eral essentially different 
characters are combined represent the terms of a series of combinations in 
which the developmental series for each pair of differentiating characters are 
associated. It is demonstrated at the same time that the relation of each pair 
of different characters in hybrid union is independent of the other differences 
in the two original parental stocks. 

If n represents the number of the differentiating characters in the true 
original stocks, 3" gives the number of terms of the combination series, 4" 

1 Bateson, Mendel's Principles of Heredity, p. 57. 

2 Ibid. p. 57. 3 Ibid. pp. 64-65. 



HEREDITY 521 

the number of individuals which belong to the series, and 2" the number of 
unions which remain constant. The series therefore embraces, if the original 
stocks differ in four characters, 3* = 81 classes, 4* = 256 individuals, and 
2"* = 16 constant forms ; or, which is the same, among each 256 offspring of 
the hybrids (differing in four characters) there are 81 different combinations, 
16 of which are constant.^ 

All constant combinations which in peas are possible by the combina- 
tion of the said seven differentiating characters were actually obtained by 
repeated crossing. Their number is given by 2'' = 128. Thereby is simul- 
taneously given the practical proof that the constant cJiaractei's which appear 
in the several varieties of a group of plants may be obtained in all the asso- 
ciations which are possible, according to the {^mathematical') laws of combina- 
tions, by means of repeated artificial fertilization. 

All this has a distinct bearing upon the question of varieties, 
and its general trend is that changes effected by crossing tend 
not to remain constant ; that is, that a union of dissimilar char- 
acters by this means is practically impossible. 

It will be noted that Mendel makes no prediction as to what 
hybrids or crossed forms will look like, but only as to their 
"essential constitution" and breeding powers. 

Gametic purity. This raises the whole question of gametic 
purity as the most fundamental question involved in Mendel's 
law. If BR, when bred with BR, in actual experience produces 
not more BR's but rather B'^ -\- 2 BR -f I^, then it raises an 
interesting point as to the real nature of the germs arising from 
the crossed parents BR. 

If the characters B and R had made a real union, or blend, in 
the germ, such a distribution among the offspring would be 
impossible. The crossed or blended forms would themselves 
breed true, that is to their own type. If they do not breed true, 
then we conclude that the real cross, or blend, has not been 
made, and that in some way the characters B and R must remain 
distinct in the germinal matter of the mixed parent ; that is to 
say, the distribution of the offspring of hybrid parents into two 
classes, pure forms and hybrids, instead of one form all hybrids, 
is possible only upon the assumption that tJie tzvo characters 
remain distinct in the parents and in the germ cells thrown off 
by them, so that the elements are still capable of uniting under 

1 The student may test this formula by making the complete expansion. 
See Bateson, Mendel's Principles of Heredity, p. 64. 



522 TRANSMISSION 

the law of chance. This means that cacJi parent produces S7icces- 
sively germ cells of both characters [B and R), so that hybrid 
forms produce pollen, spermatozoa, ova, etc., of both original 
kinds, which thereafter combine by the law of chance ; that is, 
B of one parent unites with either i? or i? of the other, produc- 
ing either pure B's or BR's, ; and also, in a large number of 
instances, some y?'s unite with j9's, producing hybrids, and others 
with R's, producing pure R's from hybrid parents. This is the 
theory of gametic ^ purity, an assumption necessarily involved as 
a fundamental conception in Mendel's law, which, in the opinion 
of Mendel himself, applies only to characters that do not blend. 

Proving or disproving Mendel's law. A good many investi- 
gators are trying, often with numbers inadequately small, to 
prove or disprove Mendel's law as a general principle of hered- 
ity. It may not be out of place to call the attention of the 
student to the uselessness of this attempt, and to direct his 
attention to the problems connected with this question which 
really call for further and much-extended study. 

First of all, Mendel's law as a general proposition needs no 
further proof. The experiments on which it was founded have 
been carefully repeated by De Vries, by Correns, and by Tscher- 
mak, who agree as to the correctness of his results. They have 
been repeated upon many other species, with uniform results in 
most cases, and no new evidence is worth noting that is not 
founded on new species and that does not involve relatively 
large numbers. 

Besides all this, the fundamental conception of Mendel's law 
rests, like Gal ton's law of ancestral heredity, upon the inevitable 
mathematical relations in reproduction as outlined in the previous 
section. This " law " arises, therefore, as a special case out of 

^ The term " gamete " is coming to be used, as synonymous with "germ cell," 
to mean the unfertilized germ, ivithoiit regard to sex. When it is fertilized it is 
spoken of as a zygote. 

Thus, in the language of these terms, we should say that each hybrid parent 
produces two kinds of gametes, B and H, or dominant and recessive, or whatever 
characters have been combined. Now some gametes of the B kind will unite with 
gametes B, producing zygotes BB (pure) ; others will unite with B gametes, pro- 
ducing zygotes BB (crossed) ; and still other A' gametes will unite with B gametes, 
producing zygotes BB (also pure). Of mathematical necessity, for an entire popu- 
lation these proportions will be as i BB : 2 BB : i BB. 



HEREDITY 523 

the general principle that the binomial coefficients represent pop- 
ulations in general. If there is no blend, then the coefficients 
represent the proportions of distinct character elements. If a 
blend has occurred, then the coefficients still represent the pro- 
portions within the blend. There is and can be no uncertainty 
upon this feature of the case. The dominance of some characters 
over others is a matter of common observation and may be 
accepted as a matter of common sense. 

The feature of Mendelism on which further light is needed is 
the matter of gametic purity, a biological element of the prob- 
lem whose universal truth is not yet established, but which seems 
necessary to a rational explanation of the law as to separation 
into distinct forms ; indeed, Mendelism in its present form seems 
to mean substantially that hybrid individuals do not produce 
hybrid germs, but rather that they produce successively the 
pure germs of both lines of parentage. 

It maybe considered that Mendel's law is well established for 
certain characters ; that is, for characters that blend. This may 
be, however, only another way of admitting its truth for those 
species which maintain gametic purity — those in whose germs 
the different characters do not mix (blend), or in which, if they 
do mix, the process is very slow. This in turn is another way 
of saying that Mendel's law is a demonstrated fact, the only 
unanswered question being, To what species and characters 
does it apply ? and the answer to this depends upon the extent 
of gametic purity. In the opinion of the writer this is the 
great unanswered question, and here is the object of inquiry 
toward which all investigation of Mendel's law should be 
directed, namely, to discover to what species and to what char- 
acters its applications are limited. 

Upon this point it is worth while to note that crossed forms 
fall into one of three classes, so far as appearances are concerned : 
(i) the hybrid may resemble one of its "pure" parents so 
closely as to be indistinguishable from it ; (2) it may be a kind 
of intermediate between the two (different) parents ; (3) it may 
be quite distinct from either parent. 

Of these three classes the first is clearly Mendelian, while the 
second and third are doubtful, — the second exceedingly so. 



524 TRANSMISSION 

Both the second and third, especially the former, suggest a 
blend, and there is much in the experience of breeders to indi- 
cate that certain characters do blend, making a successful union, 
entirely against Mendel's law, whose operations indicate the 
non-formation of stable hybrids. 

The writer ventures to urge, therefore, not the attempt to 
prove or disprove this great principle, but the endeavor to learn 
and define the limits of its action. That it applies to crosses 
generally there is the greatest reason to believe, and to its gen- 
eral truth many a breeder can testify, when he has seen some of 
his favorite productions revert to their original forms before his 
very eyes. 

Experiments in crossing Japanese waltzing mice with albinos. ^ 
Darbishire conducted extensive experiments with this cross, 
producing thousands of individuals, which are fully classified in 
the original, to which reference is here made. It is more work 
of this kind that is needed. Space forbids giving more than a 
brief outline of some of the more characteristic conclusions of 
the experimenter : 

1. When the race of waltzing mice is crossed with albino mice which do 
not waltz, the waltzing habit' disappears in the resulting young, so that 
waltzing is completely recessive in Mendel's sense ; the eye color of the 
hybrids is always dark, the coat color is variable, generally a mixture of 
wild gray and white, — the character of the coat being distinctly correlated 
with characters transmitted both by the albino and by the colored parent. 
There is thus no proper dominance in Mendel's sense, so far as eye color 
and coat color are concerned, the hybrids differing always in age, color, and 
generally in coat color, from both parents. 

2. When the hybrids produced from the cross described are paired 
together, the resultant young exhibit a segregation into three groups so far 
as eye color and coat color are concerned, into two so far as regards the 
waltzing habit. The phenomenon of segregation is closely similar to that 
described by Mendel ; and in color, whether of eyes or of fur, the propor- 
tions are closely identical with those observed by him, — a quarter of the 
young resembling their albino grandparents, half representing their hybrid 
parents, and a quarter resembling their waltzing grandparents in so far that 
they have pink eyes and the same-colored fur, but differing from any of 
their immediate ancestors in the range of coat color exhibited. The pro- 
portion of individuals which exhibit the waltzing habit is less than one fifth 
of the whole number of young, and is not a Mendelian proportion. 

1 BioDietrika, Vol. Ill, Part I, pp. 1-51. 



HEREDITY 



525 



3. When hybrids are paired with albinos, half the young produced 
resemble their albino parent, half resemble their hybrid parent. This result 
is in accord with Mendel's theory. 

Darbishire adds : " There is no evidence that any individuals 
which could be properly described as ' pure dominants' or ' pure 
recessives ' exist among the whole series produced." 

The reciprocal cross. In Mendel's experiments generally recip- 
rocal crosses, according to all accounts, gave identical results. 
We know that as a general principle this does not always hold. 
For example, the common mule, which is the product of the 
male ass and the female horse, is said to be quite different from 
its reciprocal cross, the hinny, which is the product of the male 
horse and the female ass. The one is valuable, while all horse- 
men seem to agree that the other is lazy and worthless. How 
much of this is fact and how much is tradition is doubtless some- 
what uncertain. 

SECTION XIV — THE LAW OF ANCESTRAL HEREDITY 

We have abundant evidence that in a large sense the off- 
spring is the product of something more than the immediate par- 
ents. The fact of resemblance to ancestors more remote than the 
parents, and the additional fact that successive offspring of the 
same parents are not alike but form an array not very different 
from that of offspring in general, — these facts alone show us 
either that the ancestors beyond the parents contribute something 
to the offspring, or — which is the same thing — that characters 
are made up out of elements that are handed down from parent 
to offspring and from which many and various combinations 
are possible in succeeding generations and even in the same 
generation. 

The interesting question now arises. How are these liereditaiy 
influences back of an individual distributed among his ancestors 
of various degrees of consanguinity, from his immediate parents 
backward ? 

Manifestly the answer to this question is beset with many 
difficulties. We could secure a rough approximation by working 
out the coefficient of heredity between offspring and parent, 



526 TRANSMISSION 

between offspring and grandparent, and so on indefinitely ; but 
it would need to be done for each character separately. This 
involves immense labor, and, moreover, we do not ordinarily 
possess sufficiently accurate information about ancestors back 
of the parent to enable us to make such calculations. We 
seek, therefore, some expression for this relation, and such 
an expression when generalized would constitute a law of 
ancestral heredity. 

How much influence belongs to each separate ancestor ? If 
inheritance is from the race, or in a more particular sense from 
the family group, then, in practical breeding affairs, we need a 
measure of the influence of each ancestor in order to know how 
much importance to attach to the parent and how much to 
attach to the several ancestors back of the parent. 

One generation back the total heritage rested in the two 
immediate parents, and, roughly speaking, is to be regarded as 
divisible equally between them. Two generations back it rested 
in four grandparents, and, again waiving considerations of pre- 
potency, one fourth of the heritage came from each. The third 
generation back the heritage was divided among eight great- 
grandparents, presumably, on the average, equally, — that is, 
one eighth coming from each. Still another remove, and no less 
than sixteen great-great-grandparents contributed to the stream 
that made the final heritage, and it is fair to assume that each 
individual contributed its share, namely one sixteenth. 

Now these same sixteen individuals have contributed also to 
the production of many other lines of descent. If we had all 
the descendants of these sixteen great-great-grandparents of the 
particular individual we have in mind, they would constitute a 
large population, and we have no knowledge as to where, in their 
frequency distribution with respect to the character in question, 
our special individual might be found. But of all the descendants 
of these sixteen great-great-grandparents only eight of the next 
generation contributed to the production of the individual we 
have specially in mind ; again, in the next generation, only four 
have so contributed, and, last of all, out of the large population 
descended from these sixteen ancestors, two only have produced 
our individual. Now the law of ancestral heredity is designed 



HEREDITY 



527 



to enable us to predict what, on tJie average^ should be the 
product of this selected ancestry. 

Inheritance complex. The heritage from the parent is not 
therefore a simple thing, but rather a complex stream, or, more 
properly, two streams that meet from different directions, each 
made up of currents contributed from many tributaries. How 
much now has each tributary (ancestor) contributed to the 
general and composite mixture that we call the heritage 1 

Galton ^ made the first attempt to answer this question, and 
announced as the law of ancestral heredity that the two immedi- 
ate parents contributed between them one half (0.5) of the 
effective heritage, the grandparents one fourth (0.5)2, the great- 
grandparents one eighth (0.5)^, and so on, so that the effective 
contributions of the successive generations would be represented 
by the fractions 4^, i, l, -jL, etc., and the total heritage would 
be represented by the sum of these fractions, which, extended 
to infinity, would equal i, thus accounting for the total heritage. 

This general laiv applies to generations, not to individiial 
ancestors, and these fractions should be still again divided by the 
number of ancestors in each generation in order to determine 
the fractional share contributed by each individual ancestor. 
The following table exhibits the fractional contribution of each 
generation and of each individual ancestor according to the law 
of ancestral heredity as stated by Galton. 

Effective Heritage contributed by Each Generation and by 

Each Separate Ancestor according to the Law of 

Ancestral Heredity as stated by Galton 





Generation 
Backward 


Effective Contribution 
OF Each Generation 


Number of Ances- 
tors Involved 


Effective Contribution 
of Each Ancestor 


I 
2 

3 
4 

5 


\ or 0.5 
i or (0.5)2 
1 or (0.5)3 
-h or (0.5)* 
3L or (0.5)5 


4 

8 

16 

32 


ior 25.0% 
TffOr6.25% 
J5 or 1.56 -f % 
256 or 0.39 -f % 
T()Vt or 0.09 -f % 



^ Galton, Natural Inheritance, pp. 134-137 ; Proceedings of Ihe Royal Society, 
LXI, 402. 



528 TRANSMISSION 

This series (k, \, |, jq, etc.) carried to infinity would account 
for the total heritage, and if these fractions are correctly taken 
the influence of each separate ancestor would, on the average^ 
be represented by the fractions in the last column. 

This " law," at first somewhat arbitrarily derived, and an- 
nounced with considerable hesitation, has received general sup- 
port from later investigations, and all researches, mathematical 
as well as otherwise, tend to establish its substantial accuracy. 
The first announcement was based upon studies in stature. 
Somewhat later opportunity was afforded to make exhaustive 
studies from a large number of Basset hounds of distinct colors 
and of several generations of known ancestry. This study is 
reported in full by Galton,^ and the results conform substantially 
to the "law," which, as Galton observes, is "strictly consonant 
with the observed binary subdivisions of the germ cells, and the 
concomitant extrusion and loss of one half of the several contri- 
butions from each of the two parents to the germ cell of the 
offspring.^ 

These Basset hounds were especially favorable for a study of 
this kind. They are of two colors only, "lemon and white," or 
they may be marked in addition with a third color (black), in 
which case they are known as tricolor. 

It is said that individuals are distinctly of one or the other 
class, and that transitional specimens are very rare. The pedi- 
grees and color descriptions had been carefully kept by Sir 
Everett Millais, who had originated the particular stock. 

Some 8i6^ hounds of known color were descended from 
parents of known color; in 567^ cases the colors of the grand- 
parents also were known, and in 188 cases the colors were known 
for three generations back. Assigning fractional values to 
parents, grandparents, etc., according to Galton's law of an- 
cestral heredity, and calculating what the descendants shoicld be 
under the law, it appeared that, according to theory, there should 
have been 180 tricolor hounds descended from those whose 
ancestors were known for three generations. In fact, 181 such 

1 Proceedings of ike Royal Society, LXI, 401-412. - Ibid. p. 403. 

3 Not 817 and 577, as printed. There seems to be an error of i in the first row. 
Proceedings of the Royal Society, LX, 409. 



HEREDITY 529 

individuals were found, thus furnishing additional evidence <jf 
the remarkable agreement between theory and fact in matters 
of breeding, and tending strongly to establish this law. 

All things considered, the fraction i- seems to be fairly well 
established as the ratio of the intensity with which, on the 
average, characters are transmitted at the several matings in 
bisexual reproduction ; and if this be so, the law as stated by 
Galton may be accepted as substantially correct, especially 
when we recall the fact that this (| + 4 + ^ + i^ . . . to infinity) 
is the only infinite series whose ratio is |- and that will add up 
to unity, thus exactly accounting for the full heritage. 

Pearson's method.^ Pearson has treated the same problem by 
somewhat more complete mathematical methods, and arrives at 
a somewhat more general result, but a result which may be said 
to agree substantially with that of Galton. He begins by dealing 
with the question of biparental inheritance. Then by extending 
the results obtained he accounts for the total heritage from each 
generation of back ancestry, taking i?ito consideration the vari- 
ability of the entire popuhition to which each generation of the 
ancestry belongs ; that is, he considers the variability of the 
separate generations of ancestors, — a factor which Galton did 
not take into account. 

Biparental inheritance. Starting out with the question of bi- 
parental inheritance, the problem, stated in general terms, is 
as follows : What, on the average., is the character of offspring 
of fathers whose deviation from the mean of fathers in general 
is /^j, mated with mothers whose deviation from mothers in 
general is Ji^ } ^ 

In the discussion of this problem let the deviation of this 
offspring from offspring in general be //g, and its standard 
deviation (in its own array) be denoted by E. 

1 Proceedings of the Royal Society, LII, 1898, 386-412 ; also Pearson, Grammar 
of Science, pp. 468-481. 

- Stated in concrete terms, Wiiat is the height, on the average, of the children 
from those fathers who are, for example, two inches above the average height of 
fathers, mated with mothers who are one and a half inches below the average 
height of mothers ? In discussions of this kind the student should remember that 
males and females differ naturally in character valuations, and also that not all 
males become fathers nor all females become mothers, so that the race descends 
not from all but from a portion only of the preceding generations. 



530 TRANSMISSION 

As Pearson says, what now are h^ and S ; that is, what 
deviation from the mean of offspring in general (//g) is to 
be expected in the offspring of these particular parents, and 
what is their variability or standard deviation with respect to 
their own mean (S) ? Cast in still more general terms, the 
questions are these : How will the offspring from selected parents 
differ from offspring in general, and how will they differ among 
themselves ? 

Now these are fundamental questions in breeding, and their 
answer involves the following additional conceptions, all with 
reference to the character in question : 

1. The standard deviation for fathers in general (o-j). 

2. The standard deviation for mothers in general (o-g). 

3. The standard deviation for offspring in general (o-g). 

4. The coefficient of heredity between fathers and offspring 
reckoned as sons (r^). 

5. The coefficient of heredity between mothers and offspring, 
also reckoned as sons {r^. 

6. The coefficient of correlation (cross heredity) between 
fathers and mothers, due to assortative mating (rg). 

Galton considered that inheritance from two parents is sub- 
stantially equivalent to inheritance from a " mid-parent," which 
should be the mean of the two after transmuting the female 
values (measurements, for example) into lua/e equivalents by 
multiplying those values by the ratio of the vialc to the female 
jnean, for the character in question. 

Pearson, on the other hand, deals first with deviations, and 
by the deviations of the parents from parents in general he 
attempts to predict the deviation of their particular offspring 
from the mean of offspring in general, which is the same as say- 
ing "from the mean of the race." 

While Galton thus artificially built up a mid-parent to take 
the place of the two parents, Pearson developed first the theory 
of " biparental inheritance," taking into account the means 
and variabilities of the parents, the coefficient of assortative 
mating, and the coefficient of correlation between offspring and 
parents, thus leading to the following formula for biparental 
inheritance : 



HEREDITY 



531 



(i +^'3)0-1 V 0-2 / 

Where //j and Ji^ are the deviations of parents from the mean 
of parents for the character in question, //gf is the deviation of 
the offspring of these parents from offspring in general, o-j is 
the standard deviation of fathers from the mean of their gener- 
ation, 0-2 is the standard deviation of mothers from the mean 
of their generation, o-g is the standard deviation of offspring in 
general as to the character in question, i\ is the coefficient of 
heredity between offspring and parents (parents being taken 
as equipotent, that is, making i\ = r^, ;g is the coefficient of 
assortative mating. 

Now formula (i) may be written as follows : 

2 V 0-, y\(i +/3)o-iy 

or, again, it may be written 

(3) 

In this form the formula is made up of four factors. Of these 
the first represents the mid-parental deviation ; the second, the 
variability of mid-parents ; the third, the correlation coefficient 
between mid-parent and offspring; and the fourth, the standard 
deviation for this particular character. If, now, each of these 
factors (except o-g) be represented by a single letter, we have 
the following : 

H = - \h-^-\- — h.A = the mid-parental deviation, 
2 \ 0-2 7 

^ ; = p = the variability of mid-parents, 

V2 

i? = = correlation coefificient between mid-parent 

^ I + ''3 and offspring. 

* For derivation of this formula, see Appendix. 

t The offspring will, of course, form an array, and the //z is the deviation of its 
mean from the mean of offspring in general. 

\ This last expression is inverted because we desire to use .9 in the denominator. 




532 



TRANSMISSION 



We arc now able to put formula (i) in the form of a regression 
equation, giving the value Ji.^ as follows : 

//, = R '^ B, (4) 

which is the deviation of this special population from the mean 
of the race.^ 

This form of expression of formula (i) has the advantage of 
simplicity. Instead of the deviations {/i^ and /a^) of two parents 
with variabilities o-j and a^, we now have the deviation {//) of a 
single artificial mid-parent made by first transmuting female 
deviations into male values by multiplying by the ratio of male 
to female variabilities for the character in question and then 
taking the mean of the male and the transmuted female values.^ 
This is Pearson's mid-parental deviation (//). 

S is the portion of this formula which involves the variability 
of parents^ for it depends upon o-^ and upon the coefficient of 
assortative mating (/g), and when associated with H as it is in 
the formula it may be looked upon as expressing the variability 
of the mid-parent. 

Likewise R is the portion of the formula which involves the 
correlation between parent and offspring, and from the form of 
equation (4) it may be looked upon as the coefficient of correla- 
tion between offspring and mid-parent. 

If we neglect the coefficient of assortative mating, making 
rg = o, the following conclusions may be drawn from formulas 
(3) and (4), and the values of R and S: 

I. The variability of the mid-parent (S) is equal to that of 
fathers divided by V2.* 

1 Experimental determinations show that for most characters tlius far investi- 
gated the regression coefficient of offspring as compared with mid-parents is 
about 0.6, so that we may write, in general, /iz = 0.6 //.■ or, in other words, if a 
mid-parent deviates a certain amount the offspring may be expected in general 
to deviate 0.6 of that amount from the mean of the race. 

2 This is the - |//i -f — /lA = //of the formula. 



H'"-^;"^) 



<ri V I -)- ;'Q 

* That is, in -S' = = — '- , if assortative mating be disregarded, rs becomes 

zero and the formula becomes r- ! but V i = i, and we have — ^• 

V2 V2 



HEREDITY 533 

2. The correlation of sons with respect to mid-parents {A') is 
equal to that of sons with respect to fathers multiplied by V2.* 

We have answered the question as to the value of //g. It 
remains to answer the question as to the value of — , the vari- 
ability (standard deviation) of the array of offspring from the 
particular parents of deviations //^ and //^. If we assume as 
before that 7\ = r^, then 



2;=-»\/' 



The fuller treatment of the meaning of this formula will be 
taken up in a succeeding section on " Selection." 

We could now proceed to form a mid-grandparent in the same 
way by transmuting female values into their male equivalents 
by multiplying by the ratio of male to female standard devia- 
tions. Having four grandparents, we take the mean of the four 
values thus obtained for our mid-grandparent. Similarly this 
could be carried back to any number of generations, and we 
should thus derive a mid-parent for the first, second, third, etc., 
generations of ancestry. These can be conveniently referred to 
as the first, second, third, etc., mid-parents of an offspring. 

Formula for ancestral heredity. In terms of these mid-parents 
and their variabilities Pearson has stated, in modified and 
generalized form, Galton's law of ancestral heredity as follows : 

1 (T ^, I (T ,, I o- ,, I cr ^, 

/i = - - //^ -^ - - M, + - - //. + ■ ■ ■ + ~— B„ + ■ ■ ■ , 

2 CTx 4 0*2 o 0-3 2 a„ 

in which // is the deviation from the mean of offspring in general 
to be expected in offspring of mid-parents of successive genera- 
tions backward whose deviations were i/j, i/g, ^3, ■ ••, -ff,,', o" is 
the standard deviation of offspring in general [the o-g of formulas 
(i) to (4) ] ; and cr^, a^, o-g, • • ■,'a-,,, etc., are the standard deviations 
of the mid-parents of successive generations of ancestry. 

It may be noted from this formula that if we take no 
account of differences of variability in successive generations 
(cr = o-j = 0-2 = • • •), ^nd make the deviations of successive mid- 
parents equal (i/^ = ^¥3 = T/g = • • •). ^^'^ obtain Galton's series, 

* That is, in 7? = — ^ , if ;-3 be disregarded, tlie formula becomes — ^— = ^1^ 2. 

Vi+rs Vi 



534 



'JRANSMISSION 



^> i> i< i\i ' ■ ■> by which he accounts for the total heritage. This 
fractional influence of the different generations, therefore, may 
be accepted as the best general statement possible of the law 
of ancestral heredity. The influence of individual ancestors, 
waiving all considerations of special prepotency, would be found 
by dividing these fractions by the number of ancestors of that 
generation (| by 8 = -^^ for great-grandparents). (See table, 
page 527, for an extended statement of the fractional influence 
of generations and separate ancestors.) 

The variability of the offspring of an ancestry selected for an 
indefinitely large number of generations back is given by a 
formula which is merely an extension of the formula for the 
variability of the offspring of two selected parents. If we 
assume Galton's coefficients in the law of ancestral heredity, 
the formula for the general case may be written as follows : 
^2 of i\ To rg 



L 2 V2 (2 V2)- (2 ^ 2f (2 V2)" 

in which r^, i\^^ rg, • • •, r„, are the coefficients of correlation 
between offspring and the first, second, third, . . ., «th mid- 
parents. Use will be made of this formula in treating of the 
reduction of variability by selection. 

SECTION XV— LIMIT TO THE REDUCTION OF 
VARIABILITY 

We often speak of " fixing " the type by selection, meaning 
by that the reduction of variability. All recent studies, however, 
go to show that we do not greatly reduce variability by selection, 
however much we alter the type. 

In the records of corn breeding it will be remembered that, 
while the protein and oil contents rapidly responded to selection, 
yet the coefficients of variability changed but little ; ^ indeed, it 
is the experience everywhere that variability is but slightly 
reduced by selection. 

This experience accords with mathematical theory. It will 
be shown in the Appendix that, in general, the variability of an 
array is obtained from the standard deviation of offspring in 

1 See Pearson, Grammar of Science, p. 48::. 2 ggg table, p. 446. 



HEREDITY 



535 



general by multiplying this standard deviation by Vi — /-^- ; that 
is, in symbolic language, ^ = o's'^i — r^ gives the variability 
(standard deviation) of an array of offspring whose correlation 
with the selected parent is r^, and in which the variability of 
offspring in general is o-g. 

The numerical value of this variability in a given instance 
depends upon the value of Vx- Now experimental evidence 
shows that the correlation between parent and offspring ranges 
all the way from 0.3, with little or no assortative mating, up to 
about 0.5, with the highest selection of both parents that has yet 
been achieved (see table of coefficients of heredity, page 488). 

Now in our formula V =(t^^\ — r^. let us substitute these 
values : 

Whenr^ = 0.3, V =073 Vi —0.09 = 0.9539 a^\ that is, in this 
case, when one parent is selected we get an offspring only about 
5 per cent less variable than the offspring in general. 

We have already seen (page 533) that when two parents are se- 
lected, assuming them to be equipotent, the formula for the vari- 
ability of the offspring of selected parents is V = o-g^i ^ . 

Let us now make the same assumption as before ; namely, take 
}\ first as 0.3 for pangamic mating, and again as 0.5 for the case 
of perfect assortative mating. 



x^-sVi^ 



2 ; 



. 2 



If r^ = 0.3 and r^ = o, then X "^ °"3 \ ^ ^ becomes 

I + r. 



o-g \i '- = 0-3V0.82 = 0.9055 (Tg, which means that the 

selection of both parents out of a race developed by pangamic 
mating will result in the reduction of variability by only about 
10 per cent. 

2. If ^j = 0.5 and Tg = I, — that is, with perfect assortative 
mating and with the highest correlation found in highly bred 
races, — 



^^ I + ; 

becomes 



= 0-g\/l — =(J^-^\ —0.25 =0.8662 o-g,- 



536 TRANSMISSION 

all of which means that the closest selection of both parents 
(perfect assortative mating) cannot result in the reduction of 
variabihty by more than about 13 per cent. 

Moreover, if the entire back ancestry be selected, the vari- 
ability will not he much reduced below this point. In connec- 
tion with the law of ancestral heredity (page 534) we gave a 
formula for the variability of the offspring of an ancestral line 
selected back for an indefinitely large number of generations. 
This formula is 

y ^ ^., r _ _n_ _ ^2_ _ ^3 f'„_ \ . s, 

^ \ 2 V2 (2 V2)- (2 V2)*' (2 V2)" J ' 

in which S is the variability of the offspring of this selected 
ancestry, a is the variability of offspring in general for the 
population from which selection is made, and r^, 7',^, r^, •••, r,, are 
the correlation coefihcients of offspring and first, second, third, 
. . . , nth mid-parents. 

For pangamic mating, i\, r^, /-g, ■ • ■, r,^ may be taken as 

0.6 0.6 0.6 0.6 

V2' (V2)-^' (V2)3' ' (V^)"' 

Substituting these values in (i), we get 

t' = 

, r 0.6 0.6 0.6 0^6 ^ 

"^ r ~ 2^ "2(2 V^)- {^~2)\2^~2f ' (V2)''(2V2)" J 

= .^{.-o.6(l + i, + i, + ...+i, + ...)}* 

= 0.8 a\ 
^ = o- V 0.8 = 0.8944 0-, 

which means that in the case of pangamic mating the variability 
is reduced only about 1 1 per cent by selecting the entire 
ancestry. 

Basing his remarks on these facts, Pearson says that the 
10 to 13 per cent reduction obtained by the selection of two 

* The series - -\ — ,-\ — -, + ■•• to infinity is a geometrical progression whose 
4 4^ 4^^ 

sum is found in the usual manner by dividing the first term by i minus the ratio. 



HEREDITY 537 

parents is "almost the limit of the reduction of variability, even 
if the whole back ancestry be selected." He remarks, of course, 
that the new variability is from the nezv type, not the unselected 
type ; but, he adds, " coiiiiniiotis selection docs not indefinitely 
modify variability, hoivevcr vincJi it shifts the type.'' ^ 

The principal function of selection, therefore, is to alter the 
type, not to reduce vaj'iability, and the facts here cited show 
the inherent impossibility of "fixing" the type in the sense 
that individuals will not depart much from it. But, on the 
other hand, the same principle assures us that, however much 
we improve by shifting the type, there always remains sufficient 
variability for still further selection, and as long as variability 
remains there is hope and possibility for still further improve- 
ment. We may therefore fix the type by unchanging standards 
of selection, in the sense that it will remain stationary and not 
shift, but we cannot "fix" it in the sense of reducing to any 
great extent the proportion of individuals that will deviate 
from it.^ 

SECTION XVI — POWER OF SELECTION TO PERMA- 
NENTLY MODIFY TYPES BY THE ESTABLISH- 
MENT OF BREEDS 

Though selection cannot greatly reduce variability, it is yet 
immensely powerful in shifting the type, as has been shown, 
and, if long continued, in so establishing the new type that it 
will breed true thereafter without selection,^ as will now be 
shown. 

This will necessitate a variety of assumptions as to the 
ancestry back of the parent, according as our knowledge of its 
character is much or little, and according as it may be assumed 

1 Pearson, Grammar of Science, pp. 45S, 472-4S5. (Italics are mine.) 

2 Ibid. pp. 48 1 -485. 

3 "Without selection" here means absolute freedom from the influence of all 
laws but those of chance. In practice we never realize these conditions, so that 
it is always necessary to use enough systematic selection to offset the effects of 
that degree of natural selection which is found to be always at work in nature 
everywhere. What is meant is, that by continued selection we soon reach a 
point at which the inherent variability of the race is powerless of itself to alter 
the type. 



538 TRANSMISSION 

to be mediocre on the one hand or something more than 
mediocre on the other. 

Assuming mediocrity beyond some definite point in the back 
ancestry. Galton's form of the law of ancestral heredity may 
be written 

to infinity, in which h has the meaning defined on page 533. 

If the variabilities of successive generations be taken as 
equal, the fuller statement of this law as given on page 533 
reduces at once to this simple form. 

As the simpler form of statement gives a good approximate 
value, we shall, for the sake of simpHcity and elegance of results, 
be content here to investigate what grows out of this law in the 
way of establishing a character for which selection and breeding 
are being carried on. 

1. If we assume mediocrity back of the immediate parents, 
we must make 

Then h = 0.5 B^ ■ 

that is, one half the desired character is present in the offspring. 

2. If we assume mediocrity back of the grandparents, we 

must make 

B, = B,= -=o. 

Then h = o.s B, + 0.2s B.. 

If we have a fixed standard of selection, B^— B^^ and 

h = 0.75 A- 

3. If we assume mediocrity back of the great-grandparents, 

we must make 

Hi = B,^ o. 

Then /i = 0.3 B, + 0.2s Bo + 0.12s B3] 

and with a fixed standard of selection 

B^ = B, = B,; 

from which /^ = 0.875 -^i- 



HEREDITY 539 

If this same line of argument be carried on, so that the fourth 
generation of back ancestry is selected, 

/' = 0.9375^1- 
Likewise, if the fifth generation be selected, 

// = 0.9687 Hx- 
And if a sixth generation be selected, 

li =■ 0.9844 Hx. 

The significant point in all this is that six generations of 
selection, even on a mediocre stock, establish the selected 
character to within about 1.5 per cent. The full significance of 
this point will appear later. 

Finally, if selection of the character of deviation H^ be made 
for n generations, and if we may assume mediocrity in the 
ancestry beyond the wth generation, the amount of the charac- 
ter established is given by 

Making no assumptions as to mediocrity in back ancestry. 

It has been shown both by experimental and by theoretical 
methods that if mid-parents with character H-^ are selected, the 
offspring will, on the average, exhibit about 0.6 H'^\ of the 
character in question. The inquiring reader will ask here why 
this differs from the o.^ H^ obtained from Galton's law. It 
should be remembered that 0.5 ZT^ is what we obtained by 
assuming mediocrity back of the first mid-parents. In general, 
if we select parents of character H]^, their special ancestry will 
exhibit this character to a greater degree than ancestry in 
general from which the selection is made. It is therefore only 
common sense to expect a higher value than 0.5 H^ under the 
present assumption. 

Granting, then, if we can-make no assertion about back 
ancestry, that an offspring will exhibit 0.6 of the deviation of 

* ( I I is the sum of the geometrical progression ( — | 1 |---H )• 

\ 2"/ \2 4 8 2"/ 

t See p. 533; also Proceedings of the Royal Society, LXII, 396. 



540 TRANSMISSION 

selected mid-parents, Pearson has established,^ by the theory of 
multiple correlation, the following results : 

1. If selection be made of first and second generations of 
ancestry, with no knowledge as to back ancestry, 

h = 0.5 122 Hi -f 0.2927 H<,. 

If we have a fixed standard of selection, H^ = H^; 

then h = 0.8049 //i. 

2. If selection be made of three generations of ancestry 
under similar conditions as to back ancestry, 

// = 0.5015 //i + 0.255377:, + 0.1459 //g; 

with a fixed standard 7/^, 

/i = 0.9027 T/i- 

3. If selection be made of four generations of ancestry, 

/i = 0.5002 //i + 0.2507 7/0 + 0.1276 //s + 0.0729 7/4; 
with a fixed standard Z/^, 

/i = 0.95 14 /^'i. 

4. Similarly, for a selection of five generations, 

/i = 0.5000 //i + 0.2501 //o + 0.1253 7/3 + 0.06387/4 +0.0365 H^; 
and with a fixed standard Z/^, 
h = 0.9717 7/1 . 

5. Finally, for a selection of six generations, 

h = 0.5000 7/1 + 0.2500 Ho + 0.1250 7/3 + 0.0627 H^ 
+ 0.0319 7/5 + 0.0182 7/c ; 

and with our fixed standard H^, 

h = 0.98787^^1. 

It should be noted that the coefficients which we obtain are 
approaching more and more Galton's coefficients in the law of 
ancestral heredity, which means that if selection be carried 
on for a very large number of generations it does not matter 
whether the back ancestry of our selection be mediocre or 
abov^e mediocrity. 

' P/thi-cu/i/zi^s pf the Royal Society, LXII, pp. 397-398. 



HEREDITY 



541 



SECTION XVII— BREEDING TRUE, OR STABILITY OF A 
CHARACTER ESTABLISHED BY SELECTION 

It is the object of this section to show that if an improvement 
has been made in a population, or if a breed has been developed 
by selection, the offspring will not degenerate if allowed to 
breed among themselves without selection ; that is to say, if by 
selection a certain per cent of a character has been established 
on the average, the offspring will breed true to that amount of 
the character which has been established. 

For instance, if selection has been made for six generations 
of a character H^, the amount of this character appearing in the 
offspring, after this selection, is given by WH-^, if we assume 
mediocrity back of the six generations of selected ancestry. 
Now if these offspring with ^ of the desired character be 
allowed to breed together without further selection, their off- 
spring will exhibit the character H-^ in the amount given by 



?^i; 



-Mi^i+-^i+^i^i + ■••+- i^l -7^ 
2 \04/ 48 2' 64 

so that the first generation of offspring after selection has 
ceased will exhibit the character to exactly the extent that their 
parents exhibited it. 

Let us carry this forward another generation. Then the 
character will be exhibited in the amount given by 

which again shows the offsprijig nncJiangcd so far as the amount 
of the character is concerned ; and it is easily seen that this 
would be true if we should allow breeding to go on for any 
number of generations without further selection as to the char- 
acter in question.^ 

For the sake of completeness and generality let us consider 
the case where selection for a deviation H-^ has been made for 
;/ generations, and where the offspring so produced are allowed 

^ It is of course assumed that all forms of natural selection are also e.xcluded. 



542 



TRANSMISSION 



to mate without selection. In this treatment we shall assume 
mediocrity in this back ancestry of the n selected generations 
of ancestry. 

As was seen on page 539, the character is established in the 

amount given by ( i -_ \ 11^ , and we shall now show that if 

this offspring be allowed to breed without further selection it 

will breed true to i of the selected character. 

2" 

In the first generation of offspring after no selection we 
should have 

1 / I \ I I I 

2 y 2 / 2" 2'' 2 ' + ^ 

of the character //^ in question. 
This series may be written as 

2\ 2 / 2 \2 2' 2 / 2\ 2'/ 2\ 2'/ 2' 

The amount of the character present is therefore unchanged. 
In the second generation of offspring after no selection we 
should have 



2"/ 4 \ 2"/ 2'' 2^ 2" + - 



1/ l\l/ l\ I/I I I I 

= -I --+-I-^+ -.- + - + -3 +■•• + - 

2 \ 2 / 4 \ 2 / 2- \2 2 2*^ 2 

~2y~2") 4V 2"j 4V 2"/~' 2"' 

so that the amount of the character present is again unchanged. 
The method here used can be extended to any number of 
generations. We may show that if it be true for the rth genera- 
tion of offspring bred without selection, it will be true for the 

(;-+ i)th generation. If i -^ of the character has appeared in 

r generations, then in the next generation the -amount of the 
character should be given by 



HEREDITY 543 






2' + i 2"^-' 2 



I \ I / I 

I — — 



/ill I I \ / I 

= - + - + -3 4- ■••+- + -;. I - - 
\2 2 2 2 2/\ 2 

I . I I I II 

= I — — , Since - + — + —, + 1- — + — =1; 



which shows that i of the desired character will be present 

2" 

in any generation. Hence the stock will always breed true to 
the per cent of the character established. 

It may be remembered in the above that mediocrity has been 
assumed in the ancestry back of the ;/ selected generations of 
offspring ; but if this were not assumed, we have seen that after 
a few generations we obtain approximately Galton's coefficients. 
Hence, without assuming mediocrity back of n generations, we 
may safely say that the offspring will breed true to the amount 
of the character established by selection. 

The following table presents the amount of a character estab- 
lished by selection of 1,2, 3, 4, 5, and 6 generations of ancestry. 
To illustrate how these breed true we may take the simplest 
case where 0.6 of the character is established by selecting one 
generation. Suppose, then, that a generation is produced with- 
out selection. The amount of the character present will be 
given by 

(0.6) (0.5 122) + 0.2927 = 0.6, 

which illustrates that stability is established. 



544 



TRANSMISSION 



Effect of Continued Selection ui'on Variability and Type^ 



Number of 
Genera- 


Fractional Contribution of Ancestoks, 
Various Generations 


Ratio of 

Final to 

Selected 

Type 


Ratio of 
Final to 


tions OF 
Selection 


I 


2 


3 


4 


5 6 


Variability 




.6000 
.5122 

•5015 
.5002 
.5000 
.5000 












.6000 
.8049 
.9027 
.9514 
.9717 
.9878 


•9055 

.8946 

.8945 

.89445 

.8944 

.8944 


2 
3 
4 

5 
6 


.2927 

•2553 
.2507 
.2501 
.2500 


.1459 
.1276 

•1253 
.1250 


.0729 
.0638 
.0627 


•0365 
.0319 


.01S2 


To infinity 


.5000 


.2500 


.1250 


.0625 


•03125 


.015625 


I 


.8944 



SECTION XVIII — DURATION OF VARIETIES, BREEDS, 
AND FAMILY STRAINS 

How long can a desired breed or family be retained? There is 
a popular belief that varieties wear out, and that breeds must 
of necessity be constantly reenforced by new material or by new 
combinations to take the place of worn-out stock. 

The facts just presented, however, clearly indicate that if a 
type does not remain true indefinitely either it is the fault of 
adverse selection, accidental or otherwise, or else it is due to 
some physical or biological cause, for the type, once obtained, 
naturally breeds true. 

Again, from the fact that variability is not greatly reducible, 
we are safe in assuming that types once established by selection 
will not only remain true but are capable of sX\\\ further develop- 
ment if we bestow additional attention and selection, and that 
the upper limits of improvement are fixed, if fixed at all, by 
some circumstance other than variability. It may be biological, 
— like loss of fertility or reversal of selection, — or it may be 
mechanical, but the cause, whatever it may be, that sets a limit 
to improvement is not connected with variability. 

In the last analysis, however, we are bound to raise the ques- 
tion whether all types can be indefinitely maintained, even by the 

1 Pearson, Grammar of Science, p. 485. 



HEREDITY 



545 



most skillful methods. So far as ordinary laws of evolution go 
there is no doubt about it, and we can with confidence assert 
our ability to maintain a desirable type indefinitely ; but are 
there biological considerations outside of mere variability that 
tend to extinction ? Do species " wear out," or do they come to 
an untimely end by accident only ? 

In the opinion of the writer we do not possess sufficient reli- 
able data on this point to warrant confident assertion. It is 
probably true that species have disappeared off the earth at a 
rate not equaled by the production of new species. It is true, 
too, that among domestic animals some of the most valuable 
lines have disappeared in spite of the most energetic efforts to 
preserve them.^ In the instance given below the extinction is to 
be definitely ascribed to barrenness, — a defect perfectly well 
known to breeders, and considered by them at the time as fortu- 
nate, in the interest of high prices, they evidently not appreciating 
the inevitably fatal consequences of racial barrenness. 

On the other hand, many species have persisted from remote 
times practically unchanged in type (oaks and tulip trees), and 
as we are fully informed as to some of the causes that resulted 
in the extinction of favorites, like the unfortunate family of Short- 
horns just mentioned, we are warranted in hoping that species 
in general may be maintained indefinitely. 

The conclusion is forced upon us that reliable information is 
wanting as to whether all types can be indefinitely maintained. 
No proper attempt was made to save the Duchess family. Its 
inherent weakness was counted its chief virtue, and there could 
be but one conclusion. But was its fertility a waning character, 
which no amount of selection could have strengthened } Again 
we say that our knowledge is insufficient for the answer. 

Summary. Heredity is not the relation between the offspring 
and his parent simply, but the relation between him and the 
whole back ancestry. The characters of the individual are the 
characters of the race. Some are well developed, others are 
undeveloped or latent, but all are there in some degree. 

1 For example, the Duke and Duchess Shorthorns, the most famous family of 
any breed, — so famous that a heifer brought ^40,600 at the New York Mills sale 
in 1873. 



546 TRANSMISSION 

Different individuals of the same ancestry inherit differently, 
and in general the behavior of characters in transmission sug- 
gests that they are in some way made up of combinations, so 
that a high degree of variability is inevitable, even with the 
same elements ; as, for instance, a great variety of color effects 
can be produced with the same three primaries, — red, blue, and 
yellow. 

Some characters blend and others are mutually exclusive, 
each tending to preserve its identity. On this account, as well 
as from other causes, such as relative fertility, races often 
exhibit distinct polymorphism. Inheritance is not so much con- 
nected with sex as is popularly supposed. Characters often 
do not develop until late in life. This is not to be regarded as 
belated inheritance but as belated development. 

The only proper way to study the principles of heredity is by 
statistical methods, using groups instead of single individuals, 
from which no general conclusions can be safely drawn. 

The regression table brings out clearly the fact that like 
parents beget unlike offspring ; that, in general, the offspring 
is more mediocre than the parent, but that ior se/ec^ed ofispring 
the ancestry is comparatively mediocre ; that the coefficient of 
heredity between the nearest relatives is seldom above 0.50; 
that the mean of the offspring is not necessarily the same as the 
mean of the parent ; that the means of a race are its most fertile 
portions ; that, in general, a few offspring exceed the previous 
limits of the race, — that is, progress away from the type if 
favored by selection ; that exceptional individuals may arise 
either from exceptional or from mediocre parentage ; and that 
successive offspring from the same parents are not identical. 

Nothing is clearer than that the inevitable consequences of 
bisexual reproduction and of the manner of growth by the halv- 
ing of the cell contents is to insure that character combinations 
effected in this manner are brought together in definite mathe- 
matical proportions not far from those expressed in the expan- 
sion of a binomial. This is the real foundation of Mendel's law, 
for characters that do not blend, and it also expresses the rela- 
tive proportions of characters that do blend. 

The statistical methods of study enable us to develop the law 
of ancestral heredity, which agrees closely with experimental 



HEREDITY 



547 



evidence, and which shows the degree to which the various gen- 
erations have contributed to the results. 

Continued selection will sJiift the type in any desired direction, 
and after a few generations it will " breed true " in its nezv form. 
As variability is not greatly reduced by selection, there is ahvays 
opportunity for improvement so far as variability is concerned. 

Special Exercises 

1. Exercises in great variety in forming regression tables and in deducing 
the conclusions. 

2. Investigations into the operations of Mendel's law, by the examina- 
tion and identification of laboratory material and if possible by the actual 
raising of crossed forms for the purpose. 

3. Special and definite applications of the law of ancestral heredity 
to the problems of the breeder, especially in crossing, grading, and line 
breeding. 

ADDITIONAL REFERENCES 

Alternative Inheritance. By Karl Pearson. Proceedings of the 

Royal Society, LXXII, 505-510. 
American Trotting Records as Data for Heredity Studies. 

By Francis Galton. Proceedings of the Royal Society, LXII, 

310-315. 
Bateson on Pearson's Conception of Heredity. Proceedings of 

the Royal Society, LXIX, 193-205 ; Pearson's answer, LXIX, 450. 
Chances of Death. By Karl Pearson. Science, VI, 328-330. 
Contribution of Several Ancestors to Offspring. By Francis 

Galton. Proceedings of the Royal Society, LXI, 401-413. 
Correlation between Longevity and Fertility. By Karl Pear- 
son. Proceedings of the Royal Society, LXVII, 159-179, 333-337. 
Criterion to Test Theories of Heredity. By Karl Pearson (1904). 

Proceedings of the Royal Society, LXXII I, 262-280. 
Do Varieties Run Out.? By J. Craig. Gardening, 1899, pp. 278-279 j 

also in Experiment Station Record, XI, 152. 
Experimental Evidence upon Mendel's La\v. By L. H. Lock. 

Nature, LXX, 601-602 ; by Karl Pearson, 626-627. 
Experimental Studies in Heredity. Corn Report of the Royal 

Society, 1902, p. 160 ; also in Experiment Station Record, XVII, 634. 
Experimental Zoology. By T. H. Morgan. Chapters VI and VII, 

pp. 66-166. 
Experiments in Crossing White and Black Oats. By J. H. Wilson. 

Nature, 1904, p. 413; Experiment Station Record, XVI, 462. 



548 TRANSMISSION 

Eve Color in Man. Philosophical Transactions of the Royal Society, 
CXCV, A, 79->50- 

Formula for Regression. By Pear.son and Yule. Proceedings of the 
Royal Society, LX, 477-489. 

Heredity of Coat Characters in Pigs and Rabbits. By W. E. 
Castle. Science, XXI, 737-738, 986. 

History of the Development of the Quantitative Study of 
Variation. By C. B. Davenport. Science, \TII, 864; Proceedings 
of the American Association for the Advancement of Science, 1900, 
XLIX, 197-200. 

Hybrid Oranges. By Webber and Swingle. Science, XVII, 262- 
263. 

Hybrid Wheats. By W.J. Spillman. Bulletin No. 115, Office of Ex- 
periment Stations; also in Science, XX, 68. 

Inheritance in Coat Color, Thoroughbred Horses. By Blan- 
chard. Biometrika, I, 361-364 ; by Karl Pearson, Philosophical 
Transactions of the Royal Society, CXCV, A, 1-49. 

Inheritance of Fertility. (Race horses and the human race.) By 
Karl Pearson. Science, IX, 283-286. 

Inheritance of Mental Characters in Man. By Karl Pearson. 
Proceedings of the Royal Society, LXIX, 153-155. 

Latent Characters and Reversion. By W. E. Castle. Science, 

XXI, 378-379- 

Law of Ancestral Heredity. By Karl Pearson. Biometrika, II, 

21 1-229, 231-236. 
Law of Heredity. By C. B. Davenport. Science, VII, 158-161. 
Law of Reversion. By Karl Pearson. Proceedings of the Royal 

Society, LXVI, 140-164, 241-244, 316-323, 324-327. 
Laws of Ancestral Heredity. By Karl Pearson. Science, VII, 

337-339' 551-554- 

Laws of Heredity of Galton and Mendel, and Some Laws 
Governing Improvement by Selection. By W. E. Castle. Pro- 
ceedings of the American Academy of Arts and Sciences, XXXIX, 
22 1— 242. 

Limits of Variation in Plants. (Author says variation is in mathe- 
matical ratio.) By J. W. Harshberger. Science, XIII, 251. 

Longevity and the Selective Death Rate. Pearson and Beeton. 
Proceedings of the Royal Society, LXV, 290-305. 

Mathematical Contribution to the Theory of Heredity. By 
Karl Pearson. Proceedings of the Royal Society, LXXI, 288-314. 

Mathematical Evolution. By Karl Pearson. Proceedings of the 
Royal Society, LIV, 329. 

Mathematical Evolution. By Karl Pearson. Proceedings of the 
Royal Society, LXIV: Genetic Selection, 163-165; Inheritance of 
Fertility, 165-166; Inheritance of Fecundity, 166-167. 



HEREDITY 



549 



Mathematical Evolution and Mkndkl's Law. By Karl Pearson 

(1904). Philosophical Transactions of the Royal Society, CCIII, A, 

53-86. 
Mathematical Evolution — Correlation. By Lee and Pearson. 

Proceedings of the Royal Society, LXI, 343-356; LXII, 173-175, 

386-417; LXI 1 1, 417-419. 
Mathematical Evolution — Some Errors to be Avoided. By 

Karl Pearson. Proceedings of the Royal Society, LX, 489-498 ; On 

Spurious Correlation, 498-502. 
Measuring Variations in Animals. (Report of a committee of 

Gallon and others.) Proceedings of the Royal Society, LVII, 

360-382. 
Mendelian Inheritance of Three Characters. By William Bateson. 

Proceedings of the Cambridge Philosophical Society, XII, 153-154. 
Mendelism. (Experiments with guinea-chicken hybrids.) By M. L. 

Snyder. Science, XXI, 854-855. 
Mendel's Law. (Angora goats.) By W. E. Castle. Science, XVIII, 

760-761. 
Mendel's Law. By A. I). Uarbishire. Experiment Station Record, 

XVI, 232. 
Mendel's Law (Exceptions to). By W. J. Spillman. Science, XVI, 

709-710, 794-796. 
Mendel's Law. (Experiments with mice.) By C. B. Davenport. Science, 

XIX, I lo-i 14. 
Mendel's Law and Cvtological Investigation. By C. B. Wilson, 

Science, XVI, 991-993. 
Mendel's Law and Negro Albinism. By William C. Larrabee. 

Science, XVII, 75-76. 
Mendel's Law. Defense by Bateson. Cambridge University Press 

1902, p. 212 ; Experiment Station Record, XIV, 634. 
Mendel's Law, — Discussion, Defense, and Criticism. Biometrika, 

1902, No. 2, pp. 228-254 ; Journal of the Royal Horticultural Society, 

1902, pp. 688-695 ; Experiment Station Record, XIV, 446-447. 
Mental and Moral Heredity in Royalty. By Dr. F. A. Woods, 

Harvard University. Popular Science Monthly, LXI, three articles; 

LXII, six articles. 
New Evidence for Individuality of Chromosomes. By W. J. 

Baumgartner. Biological Bulletin, VIII, 1-23. 
On the Influence of Selection in Variability. By Karl Pearson. 

Proceedings of the Royal Society, LXIX, 330-332. 
Origin of Black Sheep in a Flock (Mendelian). By C. B. Daven- 
port. Science, XXII, 674-675. 
Purity of Germ Cells. By T. H. Morgan. Science, XXII, 877-879. 
Regression and Inheritance in the Case of Two Parents. 

Proceedings of the Royal Society, LVIII, 240-242. 



550 TRANSMISSION 

Regkkssion, Heredity, Panmixia. By Karl Pearson. Proceedings of 

the Royal Society, LIX, 69-70. 
Reproductive Selection. By Karl Pearson. Proceedings of the 

Royal Society, LIX, 301-304. 
Second-Generation Hybrids. By Halstead and Kelsey. New Jersey 

Experiment Station Report, 1902, pp. 377-395 ; Experiment Station 

Record, XV, 152. 
Skew Variation. By Karl Pearson. Proceedings of the Royal Society, 

LVII, 257-260. 
Statement of Mendel's Law. (With bibliography.) By W. E. Castle. 

Science, XVIII, 396-405 ; also by L. H. Bailey, XVII, 441-454 
Telegony in Man. By Karl Pearson. Proceedings of the Royal 

Society, LX, 273-283. 
The Statistical Study of Evolution. By C. B. Davenport. 

Popular Science Monthly, LIX, 447-460. 
Variability of Individual and Race. By Karl Pearson. Proceed- 
ings of the Royal Society, LXVIII, 1-5, 372-373. 
Variation and Correlation in Man — Civilized as Compared 

with Primitive Races. By Karl Pearson. Science, VI, 49-50. 
Wonder Horses and Mendelism. (Several generations of horses 

with very long manes and tails.) By C. B. Davenport. Science, XIX, 

151-153- 



CHAPTER XV 

PREPOTENCY 

That all parents are not equally powerful in impressing 
racial characters is a fact well known to the merest novice in 
breeding. It is distinctly shown in all regression tables, and 
the reason for it is clearly seen in the mathematical nature of 
reproduction, by which individuals are differently endowed, and 
by which some few are exceptionally rich in the elements out of 
which racial characters are developed. When to these facts is 
added the difficulty of selecting animals by outward appearance, 
on account of the relation of dominant and recessive characters, 
we need feel no surprise at the relatively small number of 
highly prepotent individuals and the large number of reversions 
encountered in actual breeding. 

SECTION I — DATA FROM THE TROTTING RECORDS 
ILLUSTRATING PREPOTENCY 

Seeking material which would illustrate accurately, and with 
sufficiently large numbers, the differences in the breeding powers 
of different individuals, the writer made some studies in the 
records of trotting-bred horses. These studies covered all 
animals registered and that had made track or breeding records 
from the opening of the Register and the Yearbook down to 
and including the year 1901.^ 

In the consideration of this material, and in the comparison 
of individuals, four facts must be borne in mind : first, some 
individuals were too young for their full breeding record to be 
all in ; second, some had enjoyed less opportunity than others, 
owing to their racing engagements ; third, some stallions had 
access to better mares, and more of them, than had others ; 

^ It is needless to say that this proved a laborious task, covering many weeks, 
with two calculators. 

551 



552 



TRANSMISSION 



fourth, fashion has much to do, even among race horses, in 
influencing selection, especially after an individual or a family 
has acquired a reputation. 

Allowing as fully as possible for these facts, the records are 
worth study for the light they throw upon the question of 
inherent differences between individuals in respect to breeding 
powers — differences so great that as we proceed it will be 
perfectly evident that the line of descent runs through few 
individuals and quite independent of the mass. 

The total number of performers listed — that is, that had 
made track records good enough to admit them to the 2:30 list 
at this date (1901) — was 26,327, of which 17,625, or almost 
exactly two thirds, were trotters, and 8702 were pacers. 

The Register showed that, in all, 34,299 stallions had been 
recorded at this time, but the breeding record showed that only 
6278, or less than one in five, had produced anything in the list; ^ 
that is to say, roughly speaking, 6278 sires had produced 26,327 
performers, or an average of 4. i + each. 

Great sires. Of these 6278 sires only 207 had produced ten 
or more sires or dams of speed; that is, only 207 had bred well 
enough to produce either ten stallions each, or ten mares each, 
capable themselves of producing speed. ^ In other words, of the 
whole 34,299 stallions and 6278 sires, only 207 bred speed well 
enough to send it into the second generation to the extent of 
either ten sires or ten dams producing speed. 

Now these 207 great sires themselves produced directly 5377 
performers (4226-1 151 p.),^ which is tnore than one fifth of 
the entire list of performers^ and an average of 26 apiece, or 
six times the breeding record of the average stallion. 

Again, these 207 great sires produced 3155 sires of performers, 
and they in turn produced 16,536 trotters and pacers (11,737- 
4799 P-)- This is over half of all the sires and over 62 per cent 
of all the performers of the breed. 

1 This was partly, as has been aheady noted, because some individuals were too 
young to have made a full breeding record. 

- This, of course, does not include those sires whose produce in sires and dams 
together equaled ten. 

•' Note that 4226—1151 p. means 4226 trotters and 1151 pacers. 



PREPOTENCY 



553 



Besides this, these same 207 sires produced 4507 dams of 
speed, and ///reproduced 6691 performers (51 20-1 571 p.); so 
that about 3 per cent of the sires have produced the sires 
and dams of somewhere between two thirds and three quarters 
of the total speed of the race. If we should add the produce of 
the sires and the dams, we should have 16,536 + 6691 = 23,227 
apparent grandchildren of those 207 sires. This we cannot do 
because many of those recorded as offspring of dams are also 
recorded among the offspring of sires ; that is to say, they are 
duplicates due to the fact that many of the 4507 dams were mated 
with some of the 3155 sires. We cannot tell, therefore, from 
these figures what exact proportion of the total number registered 
may have descended from the 207 great sires. 

Distinction between sires of sires and sires of dams. Ana- 
lyzing these 207 great sires, it was found that they were un- 
equally divided between sires of sires and sires of dams of speed 
as follows : 

Class I. Sires of ten or more sires of speed, but of less than 
ten dams of speed, — 9. 

Class 2. Sires of ten or more dams of speed, but of less than 
ten sires of speed, — 113. 

Class 3. Sires of ten or more sires of speed and of ten or 
more dams of speed,- — 85. 

Of these three classes, i may be considered as distinctly sires of 
sires, 2 as sires of dams, and 3 as sires of both sires and dams. 

From the table on the following page it appears that : 

1. The poorest breeding record was made in every case but 
one by Class 2, — the sires of ten or more dams but not of ten 
or more sires. Note the ratios, lines 3, 5, 7, 8, 10, 12, 13, 15. 
The only case in which they outdid Class i was in the ratio of 
dams produced per stallion (15), which was clearly in excess of 
Class I (6), which are distinctly stallion breeders (line 10). 

2. The great breeding record was made by Class 3, — the 
sires that produced both sires and dams freely. In every case 
the ratios are higher than for any other class, whether performers, 
sires, dams, or produce of sires or dams. 

3. Class I, sires of sires, was clearly superior to Class 2, sires 
of dams, but in all cases inferior to Class 3, sires of both. 



554 



TRANSMISSION 



Breeding Record of Three Classes of Stallions; i, Sires of 

Sires; 2, Sires of Dams; 3, Sires of Both Sires 

AND Dams of Speed 



Class i 


Class z 


9 


"3 


274 


1357 


30 


12 


113 


461 


12 


4 


332 


1396 


3 + 


3 + 


37 


12 + 


57 


1677 


6 


15 


60 


2342 


1 + 


1-5- 


7- 


20 + 


40 


145 


4 + 


1 + 



3 
4 
5 
6 

7 
8 

9 
10 
II 
12 

13 
14 
IS 



Number of sires 

Total performers gotten directly by these sires . 

Ratio per sire 

Sires of performers gotten by each class 

Ratio per original sire 

Performers gotten by these sires (line 4) . . . 

Ratio per sire (line 4) 

Ratio to original sires(line i) 

Dams of performers gotten by original sires . 

Ratio to original sires 

Performers produced by these dams (line 9) . . 

Ratio per dam 

Ratio to original sires (line i) 

Performers (line 4) that were also sires of speed . 
Ratio to original sires (line i) 



85 

3.746 

44 

2,581 

30 

14,808 

6- 

174 

2,773 

32 

4,289 

1-5 + 
50+ 

888 
10+ 



4. One outside circumstance helps to relieve the burden of 
inferiority resting on Class 2. A stallion belonging to an un- 
fashionable line would be used but little or not at all in the stud, 
while a mare belonging to an equally unfashionable strain would 
not be equally barred. The result of this discrimination in the 
long run, and under our methods of study, would appear in the 
form of sires of dams. To some extent it means, not that these 
sires did not produce males, but that, being unfashionable, these 
males had little opportunity. This probably does not account 
for all differences, even though the turns and caprices of 
fashion are harder on sires than on dams. 

It must not be forgotten in this connection that these 1 13 sires 
constitute more than one half of the 207 greatest sires of the race. 
They could not, therefore, have been so very unfashionable. 

5. Class I must be largely what it seems to be, — breeders 
of sires rather than of dams, because there is no reason why its 
female offspring should have been suppressed. It is clearly 
superior to Class 2, but inferior to Class 3. 



PREPOTENCY 



555 



6. Class 3 evidently represents the cream of the race, — 
exceedingly prolific and highly fashionable, — the most success- 
ful getters both of speed and of breeders. 

7. These 85 sires themselves produced directly 2581 sires of 
performers (30 apiece), this number being over 40 per cent of 
all the sires of the breed. They produced directly 3746 per- 
formers, or 14 per cent of all in the list. The 2581 sires directly 
gotten by them produced 14,808 performers, or over 56 percent 
of all in the list. This means that a little over one per cent of the 
sires are grandsires to over half the breed. 

The big ten. But the highest relative excellence is well within 
these 85 great breeders. Their average get of performers was 
44, or over ten times the average of the race, but out of the 
34,299 registered stallions ten., and ten only, produced directly 
as many as a hundred or more performers each.^ The tabulation 
of the breeding record of these ten greatest stallions is good 
reading for the student of prepotency, as it shows a breeding 
power which fully justified their fame as great producers not 
only of speed but of sires and dams of speed. 

Table showing the Record of the Ten Greatest Producers 
OF Speed- up to and including 1901 





SiRK 


Sired by 


Trotters 


Pacers 


Total 


I 

2 

3 

4 

5 
6 

7 
8 

9 
10 


Nutwood 600 . . . 
Electioneer 125 . . . 
Onward 141 1 .... 
Red Wilkes 1749 . . 
Alcantara 729 . . . 
Pilot Medium 1579 . . 
Simmons 2744 . . 
Wilton 5982 .... 
Gambetta Wilkes 4651 
Baron Wilkes 4758 . . 


Belmont 64 . . 
Hambletonian 10 
Geo. Wilkes 519 
Geo. Wilkes 519 
Geo. Wilkes 519 
Happy Medium 40( 
Geo. Wilkes 519 
Geo. Wilkes 519 
Geo. Wilkes 519 
Geo. Wilkes 519 


D . 


131 
158 
124 
' 116 
102 

94 

82 
89 
49 
78 


34 

2 

34 
41 
47 
20 

23 
14 
52 
21 


165 
160 
158 

157 
149 
114 
105 
103 
lOI 

99 




Total 






1023 


288 


1311 












Average .... 






102 


29 


131 









1 One of these goes in at 99. 



- Trotters and pacers. 



i56 



TRANSMISSION 



This is 32 times the breeding record of the average sire, and 
nearly five times the record of the 207 great sires, themselves 
included, or over six times their record exclusive of. these ten. 

It is worth while to note the sires of these great breeders of 
speed. Number 2 is by Hambletonian 10; No. 6 is by Happy 
Medium, he by Hambletonian 10; No. i is by Belmont, by 
Abdallah, he by Hambletonian 10; and the remaining seven, 
Nos. 3, 4, 5, 7, 8, 9, 10, are by Geo. Wilkes, by Hamble- 
tonian 10. Thus, of this remarkable list of ten stallions, all 
except one are but two removes from Hambletonian 10. Of this 
number, those that were sired by Geo. Wilkes produced 640 
trotters and 232 pacers, — in all 872 performers, or more than 
66 per cent of the whole. 

The famous grandsires. Eight stallions of this list have the 
distinction of being grandsire to over 500 performers, as follows : 

Table of Famous Grandsires having 500 or more Performers 
IN THE Second Generation ^ 



I 


2 


3 


4 


5 


6 


7 


8 


Name 


Per- 
formers 


Sires 


Per- 
for?iiers 


Dams 


Per- 
formers 


Total Per- 
formers 


Performing 
Sires and Get 


Cxeo. Wilkes ('56-'82) . . 
Hambletonian 10 ('49-'76) 
Electioneer ('68-'9o) . . . 

Nutwood ('70- ) 

Belmont ('64-'89) 

Almont ('64-84) 

Red Wilkes ('74- ) • • • 
Onward ('75- ) 


83 

40 
160 
165 

59 

37 

157 

1 58 


102 

150 

97 

132 

74 

96 

93 
106 


2410 

1694 

942 

693 
6.5 

569 
471 
454 


96 
80 

79 

"3 

66 

81 

79 
57 


163 
117 

103 
184 
IIO 

130 
116 

91 


2573 

1811 

1045 

877 

725 

699 

587 

545 


40-1501 

8- 174 

60- 723 

55- 291 
25- 342 
14- 212 

56- 374 
34- 228 



1 Column I, name of grandsire; column 2, number of performers of /lis o-iCii 
get ; columns 3 and 4, number of sires he got, with their get in the list ; columns 
5 and 6, number of dams he got, with the performers dropped by them ; column 7, 
total performers gotten by sires and dams, — the second generation ; column 8, 
number of performers (column 2) that were also sires, and their performing get. 

N.B. Many of the sires (column 3) were not performers and many of the 
performers (column 2) were not sires. Numbers in parentheses refer to year of 
birth and death. 



PREPOTENCY 



557 



Breeders of speed and breeders of breeders. Nothing more 
forcibly strikes the student working with records of this kind 
than the fact that some sires are notably sires of speed which 
ends in that generation, while others, not specially noteworthy 
for getting performers themselves, yet produce sires and dams 
of extreme breeding power. See the following table, which is a 
table of famous producers of speed, and compare with the last 
table, which is a table of famous producers of prodiicers. Especial 
attention is called in this connection to Wilton, Simmons, and 
Pilot Medium, — famous getters of speed, — as compared with 
Almont, Belmont, Hambletonian, and Geo. Wilkes, — none of 
them famous as direct producers of speed, but all phenomenal 
breeders of sires and dams of speed. 

Table of Famous Sires and their Descendants ; being All that 
Sired ioo Performers or Over^ 



I 


2 


3 


4 


5 


6 


7 


8 


Name 


Per- 
formers 


Sires 


Per- 
formers 


Dams 


Per- 
formers 


Total Per- 
formers 


Performing 
Sires and Get 


Baron Wilkes ('82- ) . . 
Gambetta Wilkes ('81- ) 

Wilton ('80- ) 

Simmons ('79- ) 

Pilot Medium ('79- ) . . 

Alcantara ('76- ) 

Red Wilkes ('74- ) • • . 

Onward ('75- ) 

Electioneer ('6S-'9o) . . . 
Nutwood ('70- ) 


99 

lOI 

103 
105 
114 
149 
157 
158 
160 
165 


26 

30 

13 
26 

17 

43 

93 

106 

97 
132 


94 
III 

30 

63 

32 

200 

471 
454 
942 

693 


21 

17 

9 

14 

23 

27 

79 

57 

79 

113 


23 
23 
13 
18 

ZZ 

45 

116 

91 
103 
184 


"7 
134 

43 
81 

65 

3>5 
587 
545 
1045 
887 


21- 85 

"- 43 

11- 28 

13- 54 

12- 23 
1 9- 1 II 

56-374 
34-228 
60-723 
55-291 



Attention is especially called to column 7, recording the 
second generation of performers, as compared with column 2, 
— those gotten directly. It will be noted of three famous stallions 
that they were represented by fewer performers in the second 

1 This table is made up on exactly the same plan as the previous table ; it 
is designed to be studied in connection with the former, to show the difference 
between breeders of speed and breeders of breeders. Years are denoted by figures 
in parentheses. 



558 TRANSMISSION 

generation than in the first, but also that their age is against 
their second-generation record. 

Relation between performance and breeding powers. An at- 
temi)t was made to learn whether i)erformers are better breeders 
than non-performers. There were at that time 49 stallions in 
the 2:10 list. Only 21 of these had get in the 2:30 list, and 
only four had produced sires of speed. 

The breeding record of this class of stallions looks pitifully 
slim as compared with that of the great breeders. The best 
breeding record made by a horse in the 2:10 list, up to the 
time these studies were made, was that of Nelson 4209, who 
had i)roduced 28-12 p., eight sires (5-7 p.). ^'""d three dams 
(1-2 p.). The whole 49 in the 2:10 list had produced only 
194-65 p., and only 13 sires of speed, 8 of which have just been 
credited to Nelson. 

We might conclude that performance is not a very good index 
of breeding power, but it would be a hasty conclusion if made 
on this basis. Two circumstances conspire to keep down the 
breeding record of stallions of extreme speed. One of these is 
the fact that many of them are young, and the other is the fact 
that a horse capable of i!iakiuj>- low records is xvorth more for 
raciui^ than for breeding purposes, and while racing engagements 
do not absolutely prevent breeding among stallions, as it does 
among mares until their racing days are over,^ yet it operates 
to greatly reduce it. Evidently we shall get little light on our 
question from this source. 

Turning to individuals, we find that Nutwood 600, the great- 
est sire of speed (see table on page 555), had a record of 2:18 |, 
but that Electioneer, the next greatest sire of speed, had no 
record. Of the " big ten," but one has a record as good as 
2:18, and his breeding record is the lowest of the lot. 

Turning to the greatest grandsires of speed, Geo. Wilkes 
heads the list with a record of 2:22, but Ilambletonian 10 
comes next, having jn'oduced more sires of speed than any horse 

1 There were also 49 niares in the 2:10 list, — a strange coincidence, — not 
one of whom had produced anything in the list. This fact is, of course, not to be 
construed to mean that they could not produce speed, but rather that they have 
not, as a class, had the opportunity. What kind of brood mares they would make 
when tried is another question. 



PREPO'J'ENCY 559 

living or dead, and he has no reeord ; ' Electioneer 125 comes 
next, also with no record; then Nutwood, 2:1 8'] ; Belmont, no 
record; followed by Almont, 2:3951 ; Red Wilkes, 2:40; and 
Onward, 2:25]. 

From this showin<;" of individuals we can ari;ue either that the 
great breeders were too busy to make racing records or that 
breeding power is independent of the ability to j^erform. 

Neither conclusion is warranted. In the first place, the breed- 
ing record of a stallion with a track record is injured by the 
fact that he has little opportunity until his racing days are 
over ; but it is helped by the fact that when he is sent to the 
stud he has a superior class of marcs. 

Again, it does not follow, if a horse has not made a track 
record, that he should be considered as unable to do it. It may 
be from some slight defect or from lack of proper training, from 
some minor injury, or from one or more of a hundred other 
causes having no connection whatever with his inherited ability 
to go. 

Evidently, if we are to get any light upon this question from 
this source, — and it ought to be one of the best of sources for 
information of this class, — then we must obtain it from large 
numbers, in which the breeding record of those known to be 
performers is compared directly with that of those that have no 
performance record. 

Accordingly a table was prepared exhibiting the breeding 
record of 165 of the principal stallions. They were chosen from 
the list of 207 that had produced ten or more sires of speed or 
ten or more dams of speed, and included all ijidividuals tJiat Jiad 
produced both perfor^ning and 7ion-perforniing sires ^ except a very 
few, the data for which were incomplete. The table shows, first 
(column i), the total number of performers jiroduced by the 

1 It was popularly believed that Ilambletonian 10 could go \\\ about 2:40, but 
he was dead long before anybody knew his value as a breeder of speed. 

- Hy "performers" is meant those that have a track record of 2:30, or better. 
The term "non-performers" covers all without a record; it manifestly includes 
two classes, — those that might have made a record under suitable circumstances 
and those that could not have done so under any circumstances. As there is no 
way of distinguishing between these two, they are all called non-performers, and 
the table makes a comparison between those that have made a record and all others, 
able or unal)le, that have not done so. 



56o 



TRANSMISSION 



various stallions without regard to their breeding powers ; 
second (columns 2 and 3), the number of performing sires (that 
is, sires with speed records 2 : 30 or better), with their get ; 
third (columns 4 and 5), the number of non-performing sires, 
with their get. For convenience there is added (column 6) the 
track record of those stallions (of the 165) which were themselves 
"performers" ; for example, line 6: this sire made a record of 
2:23 on the track. He produced 149 performers, 19 perform- 
ing sires that got 1 1 1 performers, and 24 sires that never made 
a record on the track but that produced 89 offspring that were 
performers. The entire table, covering 165 individuals, is given 
in order that the reader may have at hand the means of making 
individual comparisons, many of which are, to say the least, 
remarkable. Names have been omitted, but the reader may be 
interested to know that line 65 is Geo. Wilkes, 70 is Hamble- 
tonian 10, 120 is Nutwood, and 121 is Onward. 

Breeding Record of 165 Leading Stallions to show the Relation 
BETWEEN " Performance and Breeding " Powers 





I 


2 


3 


4 


5 


6 




Performing 


Sires also 


Performing 


Sires not 


Performing 






Get 


Performers 


Get 


Performers 


Get 




I 


5 


2 


12 


12 


144 




2 


4 


I 


3 


4 


6 


2:30 


3 


53 


9 


29 


23 


70 




4 


16 


3 


12 


17 


yi 


2:29>^ 


5 


55 


3 


26 


5 


1 1 




6 


•49 


19 


III 


24 


89 


2 


23 


7 


59 


27 


208 


21 


105 


2 


27 


8 


8 


3 


9 


5 


1 1 


2 


24X 


9 


92 


I 


2 


I 


I 


2 


09X 


10 


6 


I 


3 


3 


3 


2 


25 


1 1 


37 


14 


212 


82 


357 


2 


29,3^4 


12 


20 


4 


19 


9 


26 


2 


29 


13 


47 


I 


I 


6 


9 


2 


26 


14 


5 


I 


I 


3 


3 




15 


47 


6 


12 


4 


8 


2 


263^ 


16 


31 


9 


31 


12 


17 


2 


21X 


17 


30 


7 


25 


5 


12 


2 


27|< 


18 


46 


6 


40 


3 


5 


2 


I6X 



PREPOTENCY 



561 





I 


2 


3 


4 


5 


6 




Performing 


Sires also 


Performing 


Sires not 


Performing 






Get 


Performers 


Get 


Performers 


Ga 


Record 


19 


32 


I 


I 


4 


4 




20 


3 


I 


7 


I 


I 




21 


66 


6 


20 


2 


5 


2:i7X 


22 


19 


2 


8 


7 


10 




23 


65 


5 


8 


2 


2 


2 : 12 


24 


99 


21 


85 


5 


9 


2:18 


25 


17 


10 


32 


13 


28 




26 


15 


3 


3 


10 


16 




27 


59 


25 


342 


49 


273 




28 


36 


5 


9 


5 


17 


2:29 


29 


8 


I 


I 


I 


I 




30 


9 


4 


1 1 


9 


13 




31 


6 


2 


6 


4 


7 


2:22j4 


32 


60 


5 


9 


42 


119 




33 


92 


15 


83 


10 


20 




34 


25 


2 


6 


I 


I 


2:i9X 


35 


45 


10 


52 


4 


13 


2 : 12:^ 


36 


9 


I 


I 


3 


3 


2:28 


37 


4 


3 


"> -7 


13 


33 




38 


55 


2 


10 


4 


10 


2:18 


39 


17 


I 


7 


18 


29 


2 : 22 


40 


14 


2 


8 


4 


6 




41 


38 


7 


88 


28 


65 




42 


35 


2 


3 


6 


8 




43 


54 


3 


5 


I 


6 




44 


57 


21 


71 


34 


1 89 




45 


51 


10 


67 


16 


32 




46 


18 


4 


II 


3 


8 


2:23^ 


47 


16 


4 


13 


7 


9 




48 


13 


2 


66 


10 


45 




49 


85 


23 


93 


15 


16 




50 


160 


60 


723 


37 


219 




SI 


33 






4 


7 




52 


65 






I 


2 


2:25X 


53 


4 






4 


5 


2:29 


54 


24 






I 


2 


2:28^ 


55 


6 






3 


8 




56 


25 


2 


3 


I 


2 


2:15^4: 


57 


22 


3 


7 


3 


4 


2:30 


5S 


15 


3 


5 


1 1 


14 





562 



TRANSMISSiaN 





I 


3 


3 


4 


5 


6 




Performing 


Sires also 


Performing 


Sires not 


Performing 


Record 




Get 


Performers 


Get 


Performers 


Get 


59 


lOI 


II 


43 


19 


68 


2:22>^ 


60 


20 


7 


19 


10 


15 




61 


15 


6 


14 


26 


Si 




62 


'5 


5 


21 


3 


3' 




63 


4 


2 


II 


12 


52 


2:23"^ 


64 


10 


I 


9 


10 


•9 




65 


83 


40 


1501 


62 


909 


2 : 22 


66 


4 


I 


2 


17 


32, 




67 


38 


8 


43 


'5 


47 


2:20>^ 


68 


12 


6 


'7 


3 


5 


2:27X 


69 


75 


II 


85 


16 


33 


2:15^4^ 


70 


40 


8 


174 


142 


2520 




71 


24 


3 


8 


9 


32 




72 


•5 


2 


4 


9 


19 




73 


28 


6 


32 


2 


3 


2:26;^ 


74 


23 


1 


4 


3 


7 




75 


15 


I 


14 


4 


II 




76 


23 


I 


5 


4 


6 




77 


46 


8 


74 


9 


40 


2:2lX 


78 


30 


2 


5 


4 


4 




79 


94 


34 


155 


31 


205 




80 


9 


15 


96 


29 


"54 




81 


4 


I 


6 


14 


36 


2:29 


82 


5 


I 


22 


I 


8 




83 


iS 


7 


20 


4 


6 




84 


10 


4 


9 


2 


2 


2 : 21 


85 


20 


I 


I 


I 


4 


2:28 


86 


7 


3 


12 


7 


25 




87 


85 


14 


172 


1 1 


12 




88 


29 


8 


19 


7 


29 


2: 2I>^ 


■ 89 


38 


I 


2 


7 


12 


2 : 16;^ 


90 


8 


I 


12 


6 


8 




9' 


2 


I 


4 


4 


5 




92 


41 


5 


43 


21 


106 




93 


40 


•3 


32 


10 


18 




94 


II 


I 


7 


10 


19 




95 


4 


I 


10 


5 


6 




96 


4 


I 


21 


3 


7 




97 


21 


2 


7 


3 


4 




98 


31 


5 


28 


12 


42 





i'Ri:i'()ri-:NCY 



.s6: 





I 


3 


3 

Performing 
Get 


4 


5 

Performing 
Get 

88 


6 




Performing 
Get 


Sires also 
Performers 


Sires not 
Performers 

12 


Kecord 


99 


3J 


7 


63 




lOO 
lOI 


24 
7 


3 


7 
6 


4 
6 


9 
8 


2 : 21 


102 


17 


I 


2 


7 


9 




104 


13 
6 


I 


3 
'3 


'> 


4 
S3 


2 : 26 ^i 


105 
106 


47 
6 


4 


1 1 
1 1 


7 
4 


'3 
10 


2 : 2134: 


107 

loS 


60 

25 


9 

5 


102 
24 


12 

52 


>9 
158 




109 
1 10 


9 
17 


7 


9 


14 
10 


43 
28 




1 1 1 


15 


I 


I 


2 


2 




1 12 


2S 


4 


6 


'5 


39 




i'3 

114 


10 
16 


1 


4 
4 


5 
4 


'9 
8 




115 


-3 


7 


52 


18 


51 




116 


14 


3 


'9 


3 


21 




"7 

iiS 


25 

5 


3 


3 

25 


2 

6 


7 
6 




1 1 9 
120 
121 


70 
1 58 


3 

55 
34 


9 

291 
228 


5 
77 
72 


22 

402 
226 


2:18^ 
2:25X 


122 


'5 


I 


4 


3 


4 




123 


24 


I 


4 


5 


10 




124 

125 
126 


-S 
1 1 

25 


3 
4 
6 


1 1 

8 
•5 


9 
3 

I 


32 
9 
I 


2:131^ 
2 : 26>4: 

2M7X 


127 


8 


I 


5 


5 


27 




128 


5 


I 


3 


2 


2 




129 


104 


1 2 


23 


5 


9 




130 


21 


2 


3 


8 


40 




131 


5' 


13 


125 


27 


55 




132 


57 


2 


3 


I 


2 


2:2lX 


133 
134 


157 
92 


5^' 
'5 


374 
64 


37 
14 


97 
89 


2:i7>^ 


•35 
136 


18 
6 


3 
3 


99 
14 


3 
'3 


4 
3' 


2 : I7>4 


137 
138 


4 
8 


I 
4 


35 


3 
7 


4 
II 


2:29^ 



564 



TRANSMISSION 





I 


2 


3 


4 


5 


6 




Performing 


Sires also 


Performing 


Sires not 


Performing 


Record 




Get 


Performers 


Get 


Performers 


Get 


139 


96 


9 


32 


6 


8 


2: 19^ 


140 


12 


2 


6 


10 


17 


2:I5X 


141 


4 


I 


2 


I 


I 




142 


85 


4 


4 


5 


6 




143 


24 


6 


16 


4 


6 




144 


13 


2 


7 


I 


3 


2:26K 


145 


34 


3 


28 


I 


I 


2:25^ 


146 


88 


13 


85 


25 


54 




147 


52 


1 1 


78 


10 


20 


2:24 


148 


42 


I 


I 


4 


II 




149 


48 


II 


38 


27 


55 




150 


22 


2 


13 


2 


2 


2:27 


151 


10 


1 


I 


8 


24 


2:22X 


152 


15 


3 


5 


9 


73 




153 


15 


I 


2 


7 


II 




154 


31 


7 


48 


12 


33 




15s 


34 


5 


14 


36 


142 




156 


II 


3 


10 


I 


4 




157 


35 


7 


42 


9 


16 


2: 19 


158 


I 


I 


I 


I 


I 




159 


65 


7 


39 


5 


12 


2:24;^ 


160 


10 


3 


82 


9 


21 




161 


103 


II 


28 


2 


2 


2:i9X 


162 


13 


5 


61 


20 


105 


2:2I>^ 


163 


38 


4 


10 


2 


3 




164 


45 


7 


27 


II 


29 




165 


32 


2 


3 


4 


6 


2:28X 




5688 


1062 


7843 


1941 


9186 





What light, now, does this throw upon our query ? We re- 
member the disadvantage occasioned to the performing sire by the 
interference of track engagements during his racing years, and 
we remember, on the other hand, the advantage that comes from 
his enhanced reputation and the superior class of mares offered. 

This table, taken as a whole, shows that these 165 leading 
stallions (being the ones of highest note that produced both per- 
forming and non-performing sires) produced 5688 offspring and 
17,029 grand offspring with track records of 2:30 or better. 



PREPOTENCY 565 

This is an average of 34.5 direct get, and the grand-get (17,029) 
covers two thirds of all in the list {26,327). It is, therefore, the 
very cream of the breed. What, now, is the breeding record of 
the performing sires of this list as compared with that of the 
non-performing .? 

The non-performing sires (1941, column 4) are almost double 
the number of the performing sires (1062, column 2). These 
1 94 1 non-performing sires produced a total of 9186 performers, 
— a ratio of 4.7 each; while the 1062 performing sires pro- 
duced in all 7843 performers, — a ratio of 7.4 each. 

If any difference in breeding powers is correlated with high 
speed, it would be reduced rather than exaggerated in this table, 
for the list of what are called non-performers clearly includes a 
good many potential performers that had the inherent ability to 
"so " if all conditions had been favorable. 

At the same time it must not be forgotten that the non-per- 
forming sires on this list are of the same blood lines as are the 
performing sires, being in every ease at least half-brothers out of 
the same sire} To the writer the conclusion seems inevitable 
that the heavy difference of 7.4 against 4.7 apiece is in a large 
sense correlated with the individual ability to "perform." 

Turning to individual cases, we find that the performing sires 
got by Geo. Wilkes (line 65) produced on an average 37.5 
performers apiece (I50I-^40), while his non-performing sires 
produced an average of only 14.6 (909 ^62), although the popu- 
larity of Wilkes' blood was enough to assure almost any son of 
his a "good chance." 

Nutwood (line 120), the greatest sire of speed, produced 55 
performing sires and yj ;/cw-performing sires. The first produced 
at the rate of 5.3 (291 h- 55) and the second at the rate of 5.2 
(402 -^77), — almost exactly the same. Onward (line 121) pro- 
duced 34 performing sires and 72 w^«-performing. The first 
produced performers at the rate of 6.7 each, the second at the 
rate of 3.1. 

Hambletonian 10 (line 70), the most successful producer of 
racing blood and the foundation of almost all modern blood lines, 

1 The table is confined to those stallions that produced both ferforviiiii:; and 
iiojt-perforniiiig sires. 



566 TRANSMISSION 

produced only 40 performers and 8 performing sires, but Geo. 
Wilkes was one of these, and the average of 21.7 (174 -^ 8) tells 
but a small part of the story of these 8 performing sires of this 
remarkable progenitor of speed. His 142 iwn-pcrforniing sires 
produced speed at an average of 17.7 each. It would be an 
interesting study to determine how the descendants of these 
142 non-performing sires compared with those of the 8 perform- 
ing sires, — a study that the writer has left to others^ or to a 
future time. 

A conservative conclusion from these data would be that per- 
formance is not an invariable index of breeding powers but that 
on the average the performers are much more likely to get speed 
than are non-performers of the same breeding. 

This difference, if it really exists, is without doubt inherent ; 
indeed, it is not difficult to find instances in which that which 
seems to be the general principle is reversed, so that the non- 
performcrs are the better breeders (see lines i, 44, 62, 79, 130, 
and 155) ; all of which shows that while good negative testimony 
may be found in a single instance, positive statements must be 
based upon a comprehensive study of large numbers. And so 
we need to go through our records and our experience carefully, 
hunting for the things that constitute ground on which pre- 
potency may safely be predicated. Without doubt purity of 
blood, in the sense of the highest possible percentage of characters 
favorable to the purpose desired, unalloyed by disturbtJig factors, 
will be found to constitute the real basis of prepotency. When 
discussing the mathematics of breeding it was found that, no 
matter what the combinations, a few individuals will always 
remain pure. By the same process of reasoning, when we mix 
the elements of desirable characters, diluting them as little as 
possible with " wild blood," we shall, by the same law of prob- 
abilities, once in a while effect a phenomenal combination. Such 
a one is produced by methods not under our control, except as 
we increase the probability by iticrcasing the intensity of breeding. 
This is the very heart and soul of " line breeding," and means 
that the best-bred animal is the most likely to be prepotent. In 

1 Work of this kind runs into days, weeks, and months, at a surprising rate. 
The data given here represent many months of laborious work. 



PREPOTENCY 567 

the meantime it will be well to remember that, to the best of our 
present knowledge, some individuals seem to be preeminently 
breeders oi performers ; others, breeders of sires ; and still others, 
breeders of dams ; while ^fezv are breeders of all three classes. 

Importance of the actual test. The student cannot fail to note 
that the bulk of the business of real improvement is done by a 
very few really great animals, and that the work of most of the 
so-called breeding stock is merely that of reproduction in the 
sense of increase of numbers. 

It is perfectly clear that he who is bent upon accomplishing 
real results will seek for the occasional phenomenal breeder, 
and, having found him, will make the most of him while he is 
able to reproduce. It is matter of deep regret that so many of 
our phenomenal animals, like Hambletonian 10, were never 
recognized as such until long after they were dead and the 
opportunity to utilize them to the best advantage had passed 
forever, leaving us to do the best we can and make the most of 
the " accidents " that are left behind. 

In seeking these phenomenal breeders too much cannot be 
said concerning the importance of the actual breeding test as 
the last and final criterion of breeding powers, — a subject on 
which more will be said later. 

SECTION II — PREPOTENCY IN SEX 

There is a traditional belief that in general the sire is pre- 
potent over the dam. In actual practice this is likely to be the 
case, for the sire is, in most cases, the better bred of the two 
parents. If a breeder starts out to breed half bloods, and to give 
his stock the most benefit possible of good blood at the least 
expense, he will of course provide it through the male side ; for 
with one male he can influence the blood of many offspring, 
while with the female he can influence but one in horses or 
cattle, and but few in swine. So it comes about, for purely 
economic reasons alone, that in general sires are better bred 
than dams, and on this account should be prepotent. 

But, the question of breeding aside, are they prepotent be- 
cause of sex 1 On this point speculation has long been at work. 



568 TRANSMISSION 

resulting in a choice collection of "beliefs," covering about all 
the combinations possible. It is held : 

1. That the male is prepotent on general principles, because 
males are stronger and more virile than females. 

2. That the female is prepotent, especially among mammals, 
because her associations with the offspring are so much more 
intimate, both physiologically and socially. 

3. That that parent is prepotent which has the stronger 
nervous and sexual organization, — whatever that may mean. 

4. That the male is prepotent over the forward and upper 
parts of the body and the mental qualities. 

5. That the exact reverse of the last statement is the truth. 

6. That the male governs the external and the female the 
internal organs and parts. 

Instances are not wanting to " prove " any of these beliefs ; 
indeed, proof by the method of instance is the favorite form of 
argument for or against any one of them, and it is not too much 
to say that by this method these or any other assumptions may 
be readily substantiated. 

We have learned long ago the unreliability of conclusions of 
this kind, and it is worth while to distinguish clearly, so far as 
we are able, between what is known and what has not yet been 
learned touching this important matter. 

In general the sexes are equipotent. So far as is now known, 
no part of the germ cell is naturally predestined to provide any 
particular part of the body. The germ cells from both parents 
are bearers of the hereditary substance in the proportion in 
which they possess it, and either sex may and does transmit 
any and all the characters of the race to its offspring of either 
sex. We may say then, in general, that that parent will be 
prepotent whose hereditary substance is least mixed and, there- 
fore, most intensified along the line of established characters. 
The only way we can go farther than the general principle just 
stated is by extensive studies solving the coefficient of Jieredity 
between each parent and its offspring of both sexes for different 
characters separately. 

This has been done for a number of characters, both in men 
and in animals, though the list is too small to do more than to 



PREPOTENCY 



569 



indicate the direction, without showing the Hmits, of prepotency. 
The following list from Pearson ^ includes the most accessible 
data covering this point. Unfortunately again, much of the 
material is drawn from studies in man, but fortunately also 
horses and dogs have been included to some extent. It is all 
useful in showing the mixed nature of prepotency. 

Table illustrating Prepotency of Sex 



Relationship 



Character 



Coefficient 

OF 

Heredity 



4 
5 

6 

7 
8 

9 
10 
II 
12 

13 
14 

15 
16 



Father and son . . . 
Father and daughter 
Mother and son . . . 
Mother and daughter 
Mother and son . . . 
Mother and daughter 

Sire and foal 

Dam and foal .... 
Sire and offspring . . 
Dam and offspring . 
Brother and brother . 
Colt '-2 and colt . . 
Sister and sister . 
Filly "" and filly . . 
Brother and sister 
Colt and filly . . . 



English 

English 

English 

English 

American Indians . . 
American Indians . . 
Thoroughbred horses 
Thoroughbred horses 

Basset hound 

Basset hound 

English 

Thoroughbred horses 

English 

Thoroughbred horses 

English 

Thoroughbred horses 



Stature . 
Stature . 
Stature . 
Stature . 
Head inde 
Head inde 
Coat color 
Coat color 
Coat color 
Coat color 
Stature . 
Coat color 
Stature . 
Coat color 
Stature . 
Coat color 



396 
360 
302 
284 

370 
300 

517 
527 
177 

524 
391 
623 

444 
693 
375 
583 



Here, in small compass, are results of studies sufficiently 
extensive to justify careful consideration. The following con- 
clusions are certainly warranted : 

I. The English father is prepotent over the mother in respect 
to stature in both sexes (see lines i, 2, 3, 4) ; but the reverse is 
true as to coat color in thoroughbred horses and in Basset 
hounds, especially in the latter (see lines 7, 8, 9, 10). The con- 
clusion of all this is that sometimes one sex is prepotent and 
sometimes the other, and, accordingly, that each character must 
be worked out by itself and for each race separately. 

1 Pearson, Grammar of Science, pp. 458, 461. 

2 By " colt " is of course meant a male foal, and by " filly " a female foal. 



570 TRANSMISSION 

2. To quote Pearson, the male scons to "inherit more" than 
the female because his coefficient of heredity is higher, with 
whichever parent the comparison is made (compare lines i, 3, 5, 
with lines 2, 4, 6). This conclusion Pearson declares is con- 
firmed by data in eye color, as well as in stature, coat color, and 
head index. ^ 

It is a significant fact that for the races and characters here 
involved the correlation between brother and brother is less than 
the correlation or similarity between sister and sister (compare 
lines II and 12 with lines 13 and 14), which means also that 
sisters resemble each other more closely than do brothers. 

3. The resemblance between members of the same sex is 
closer than that between members of opposite sexes (compare 
lines II and 13 with line 15 ; also 12 and 14 with 16). Pearson 
also declares that the same principle holds for eye color and 
head index, and he is inclined to believe it general.^ 

This author points out that this principle, if general, means 
that "inheritance in a line through one sex is prepotent over 
inheritance in the same degree with a change of sex " ; that is, 
that inheritance tends to run in sex lines, which means, to 
quote Pearson (italics and parentheses mine), " that a man in eye 
color (for example) more clearly resembles his paternal than his 
maternal grandfather (or other male ancestors) ; a woman more 
closely resembles her maternal grandmother than her paternal 
grandmother. Again, a nephew is more like his paternal uncle 
than his paternal aunt ; a niece, like her maternal aunt than her 
maternal uncle." ^ 

Future investigations will add to our knowledge in these 
matters, and perhaps modify some general statements now con- 
sidered safe, but the matter as stated above represents the best 
conclusions of those who have given most careful attention to 
the subject up to the present time. 

Comparative variability of the sexes. There has been a 
general tendency to assert that males are more variable than 
females.* This assertion has not been based on actual studies 

1 Pearson, Grammar of Science, p. 459. - Ibid. p. 459. * Ibid. p. 460. 

* See Geddes and Thomson, Evolution of Sex, pp. 12-13; Darwin, Animals 

and Plants under Domestication, I, 457 ; Pearson, Chances of Death, pp. 256-260. 



PREPOTENCY 571 

but upon the theoretical ground that males lead a more active 
life and take the lead in sexual selection. The data just cited 
seem to substantiate this assertion. For the species and charac- 
ters involved it appears that male offspring follow more closely 
the parental type than do the female, and (which amounts to 
the same thing) female offspring, or sisters, are more nearly alike 
than are male offspring, or brothers, — tending to the conclusion 
that males are more variable than females. 

Pearson,^ however, records data of an exceedingly exhaustive 
series of investigations of variability in men and women, not 
absolutely but relatively, as expressed in the coefficient of 
variability. 2 While he finds men more variable at certain ages 
and in certain characters, yet he does not find pronounced and 
decided differences, nor are these the same for different races 
of men. He concludes, on the whole, that for all races studied, 
ancient and modern, and for all characters covered by the 
studies, there is "no evidence of greater male variability, but 
rather of a slightly greater female variability." 

He finds, for example, that English men are slightly more 
variable as to height than are English women (4.07 :4.03), but 
that, among Germans, women are considerably more variable 
than men (4.26:4.02), as they are also among the French 
(4.35: 3-88). 

In the long bones sometimes one is more variable, sometimes 
the other ; thus, as to the femur, men are more variable : Libyan 
(5.05 :4.46), French (5.05 : 5.04), Aino (4.65 :4. 18), and Neo- 
lithic man (4.73 :4.5i) ; but with the ancient inhabitants of the 
Canary Islands the reverse is true (men, 4.64; women, 4.71). 
In all cases examined, except the French (men, 4.975 ; women, 
5.365), the tibia is more variable in men ; but in most cases the 
humerus and radius are more variable in women. 

1 Pearson, Chances of Death, I, 256-377. 

'^ Manifestly the coefficient of variability is the only correct estimate of com- 
parative variability, because in its calculation each instance is compared with its 
own type as a base. This is necessary, because the stature of women, for example, 
is different from that of men ; hence the two cannot be compared on any common 
basis. This is the only way, for instance, as Pearson points out, in which we can 
compare the variability of man with that of the elephant ; in any other way the 
elephant would appear more variable, because he is bigger. 



572 



TRANSMISSION 



The averages of coefficients of variability for all " long-bone " 
determinations are as follows : ^ 







Femur 


Tibia 


Humerus 


Radius 


Men 

Women 


4.82 
4.58 


5-33 
4-93 


4.88 
5.10 


4.81 
5.10 





Though these are human, not animal data, yet they involve 
skeletal measurements which are among the most fundamental 
of all organic parts, and they scarcely warrant the sweeping 
assertion that males are decidedly more variable than females. 
Pearson is entirely justified in his protest against what he calls 
this "pseudo-scientific superstition" and the sweeping conclu- 
sions involving "social and practical consequences" affecting 
" the whole of our civilization." ^ 

In body weight, both among English (men, 10.37 '■> women, 
13.37) ^^d among Germans (men, 20.67 5 women, 25.07), women 
are decidedly more variable than men.'^ 

In weight at birth, both among English (boys, 15.65 ; girls, 
14.44) and among Germans (boys, 13.567; girls, 13.278), the 
males are more variable ; but among' the Belgians the reverse 
is true (boys, 14.66; girls, 17.62). 

Data of this sort are full, but unfortunately confined mostly 
to humans. From all sources it seems that men are more vari- 
able in "height when sitting'' and in "swiftness of blow," but 
that women are more variable in " stature " (height when stixnd- 
ing), "span," "body weight," "breathing capacity," "strength 
of pull," "squeeze of hand," and "keenness of sight." 

As Pearson points out, some of these variants would disappear 
if women were subjected to the same conditions of life as are 
men, and we need to be cautious when applying these data to 
races in general, — for which future researches are sorely needed. 
We certainly are not warranted in assuming sweeping and funda- 
mental differences in variability between the sexes. Here again 

1 Pearson, Chances of Death, I, 305. '-^ Ibid. I, 256 and 376. 

^ Incidentally, the same data warrant our conclusion that the German race, 
both men and women, are more variable than the English as to body weight. 



PREPOTENCY 573 

is fertile territory for careful and exhaustive statistical studies, 
which alone will yield reliable results on which principles of 
selection and breeding may be based. 

SECTION III— INFLUENCE OF AGE ON PREPOTENCY 

Is one parent prepotent over the other merely by reason of 
age ? The question is exceedingly important, but the writer is 
not aware of reliable data bearing upon the subject. The matter 
could be determined by sufficient investigation into the offspring 
from parents with some considerable discrepancy as to age, and 
by comparing the coefficients of heredity between the offspring 
of young and those of old parents, not only with each other but 
with the normal of the race. Helpful as it would be to know the 
facts upon this point, they have not yet been discovered and it is 
idle to speculate. We have no choice but to wait until the research 
is made in what will one day constitute a prolific field for study. 

SECTION IV — INFLUENCE OF CONSTITUTIONAL VIGOR 
UPON PREPOTENCY 

This is an important question, upon which we lack reliable 
information. Common sense seems to indicate that the more 
weakly parent would not be equally influential in impressing his 
or her characteristics, but we cannot yet say to what extent the 
character of the reproductive cells is dependent on vigor. Here 
again speculation can easily run riot ; but from the fact that, 
for other reasons, we should reject the non-vigorous parent, the 
question loses most of its point except in human affairs, which 
do not concern us here. 

That one stalk in a hill of corn often resists the effects of 
frost when neighboring stalks are killed is a fact that has long 
been noted, but whether such plants are prepotent in transmit- 
ting resistance to frost is not known. It is a significant fact, 
however, that Dr. Hopkins, of the University of Illinois, when 
conducting experiments with soils containing an excess of mag- 
nesium, noticed one year a single wheat plant that flourished 
well where all others succumbed. Saving seed from this plant, 



574 TRANSMISSION 

he found its descendants highly resistant, flourishing well where 
ordinary wheat totally failed. It was, apparently, a true mutant, 
with extra strong resistance to magnesium. 

Influence of development upon prepotency. Many biologists 
contend that transmission depends to a large extent upon the 
development of the parent ; that a stallion trotting bred, for ex- 
ample, would get speed much more successfully if he himself 
were " developed " or " worked " upon the track than would the 
same stallion kept equally healthful and vigorous but not devel- 
oped as to actual speed. A natural conclusion of this contention 
is, of course, that the same sire will get more speed in his middle 
and later years than would be possible before he was developed. 

This is the very point of Casper L. Redfield's recent articles^ 
setting forth what he calls his " dynamic theory of heredity." 
He brings many instances and much argument in support of the 
assumption, but in the opinion of the writer the method of proof 
adopted is not competent to settle the question, nor is any 
method able to do so that is based upon the simple enumeration 
of instances. 

As with any other question involving great variability, the 
only way we can settle this is by employing large numbers on 
botJi sides of the proposition ; in other words, by comparing the 
speed of all the horses gotten by performing sires late in life 
with the records of the get of the same sires before development, 
or at least before long service on the track. Even then we must 
learn what deductions to make, if any, on account of differences 
in age ; after which, we may hope to learn the real effect of 
development upon prepotency. 

As the matter stands now, \.\\q. fact of prepotency is patent to 
both the casual observer and to the careful student ; but the 
reasons for this difference in breeding powers are not yet at all 
well understood. Here, as in many other directions, we await 
future studies. 

Summary. Individuals of the same ancestry differ marvel- 
ously in their breeding powers. Some can produce excellence 
directly in their own descendants, and others indirectly through 

1 See The Horseman, XXV, Nos. 19-41, on "Breeding the Trotter"; also The 
Atiiei-icaii Field, LXII, No. 25, and LXIII, No. 9, on "Evolution of the Setter." 



PREPOTENCY 



575 



sires and dams they are able to get. The Hne of descent runs 
only through the few that can produce breeders of breeders, not 
simply performers. 

Individual excellence is not a certain guide to breeding powers, 
and many ordinary individuals are among the greatest breeders. 
This is neither a mystery nor a fault in heredity ; it arises from 
the fact that individual excellence is partly a matter of individual 
development and not a sure index of real ancestral possessions. 
The specimen may be only fairly well born, though faultlessly 
developed, — in which case he will probably be a disappointment 
as a breeder ; or he may be excellently born, but only fairly well 
developed, — in which case he will breed " better than he is him- 
self " ; still again, he may be well born and perfectly developed, 
which is best of all. 

All studies yet made show that, on the average, performers 
(those individuals possessing high individual merit) are better 
breeders than non-performers ; that is, than those which do not 
show in their personal development a high degree of excellence, 
though, as we should at once surmise, there are numerous ex- 
ceptions, largely arising from our inability to accurately judge 
individuals by external appearances. 

Special Exercises 

Work out special cases of prepotency in the breeding and speed records 
of trotting and running horses, in the advanced registry of cows, and in the 
famous families of beef cattle and of swine. Pay special attention to rela- 
tive prepotency of own brothers and to the correlation between individual 
performance and breeding powers. 

ADDITIONAL REFERENCES 

A Measure of Intensity of Transmission. By Francis Galton, 1899. 

Nature, LX, 29. 
Distribution of Prepotency. (Trotting-horse records.) By Francis 

Galton. Nature, LVIII, 246-247. 
Influence of Sex on Size of Offspring. By F. B. Mumford. 

Experiment Station Record, XV, 542. 
Prepotency and Xenia. By C. Correns. Experiment Station Record, 

XI, 1016. 
Prepotency of Different Plants. By W. W. Tracy. Experiment 

Station Record, XIII, 324. 



Part IV — Practical Problems 



CHAPTER XVI 

SELECTION 

We have just seen the power of selection to fix type, providing 
it continue unchanged for five or six generations. By this we 
discover that selection is the most direct and powerful means of 
improvement at the disposal of the breeder; indeed, it would 
not be too much to say that it is the only means of permanent 
improvement that is under his direct control. 

In most phases of the breeding problem the stockman or the 
plant improver is an on-looker merely ; but in the matter of 
selection he becomes an active agent, and his decisions and his 
acts are powerful either for good or evil in controlling the des- 
tinies of the breed or the variety he handles. 

In this, to a very large extent, he supplants natural selection, 
and if he is to succeed he must be well grounded in four funda- 
mentals when he thus takes a hand in the course of nature : 

1. He must have a clear idea of what he desires to accomplish, 
and he must adhere persistently to one standard. 

2. He must be well informed as to the history of the breed 
or the variety he handles and of the variations, both new and 
old, which it is likely to afford. 

3. He must know the general principles involved in selection 
in order to know the forces with which he deals and what is 
likely to happen when he interferes. 

4. He must have judgment as to when and how far he may 
depart from sound practice on account of economic or other 
considerations. 

When we reach this phase of breeding operations we begin to 
touch financial as well as biological principles, and all this must 

577 



57S PRACTICAL PROBLEMS 

be done with reference both to what is desirable and to what 
will pay ; hence the necessity of considering all phases of the 
selection problem from a double standpoint. Each consideration 
outlined is self-evident, yet each is of sufficient importance to 
merit further consideration. 



SECTION I — IDEALS IN SELECTION 

Among the multitude of variations which every breed and 
every variety will present, the breeder must know which are 
useful. The great mass must be discarded, from the mere point 
of numbers, and no one cause of failure is more common than 
a vacillating policy regarding standards of selection. 

This uncertainty is due to no other fact than that the breeder 
does not know quite what he wants. He is " in the market " 
for "any good thing" that may turn up. In the course of his 
breeding operations a great many new and more or less promis- 
ing things will appear. Unless he has unlimited means and 
boundless space for his operations, these must be discarded 
with seeming ruthlessness, or he will speedily have an assort- 
ment of novelties which if bred among themselves will overrun 
his premises, and if bred into his permanent stock will produce 
a veritable jumble, out of which no good thing can come. In 
this way ancestry and pedigree can become so hopelessly mixed 
as to be worthless. This may happen with any breed, and even 
within the limits of purity of blood ; indeed it has happened 
over and over again, in all breeds, through the misguided enthu- 
siasm of breeders working without well-defined standards. 

Standards wisely fixed. Standards must not be left to chance. 
They must not be warped or altered by novelties, no matter how 
curious or attractive. They must be fixed in advance, like build- 
ing plans and specifications, and should be fixed in the light of 
what is needed and %vhat tJie breed is likely to afford. Indeed, 
the standards should be roughly fixed before the breed is chosen. 

Once chosen, standards should be preserved unchanged. As 
the artist sees his picture before he mixes his colors, and as the 
sculptor chips away at his marble to bring out the particular 
figure that stands in his mind, undisturbed and undissuaded 



SELECTION 



579 



from his purpose by the many other excellent figures that might 
be cut from the same material, so the breeder should adhere to 
his standards doggedly. They should be wisely chosen, it is 
true, but, once sure of that fact, and with the law of ancestral 
heredity in mind, nothing should warp the judgment as to change. 
Everything that helps to secure the ideal should be accepted, 
and everything else, no matter how attractive in itself, should 
be pushed aside, — unless, indeed, the breeder have unlimited 
means and is minded to do not one thing but many things. 

Keep blood lines pure. But if the breeder is minded to indulge 
in experiments outside the chosen standard, these experiments 
must be carried on separately. Blood lines must be kept ptirr, 
not pure within breed lines simply, but, remembering the law of 
ancestral heredity and the pull of the ancestors back of the 
immediate parent, they should be kept as pure as selection can 
make them. 

Objects of selection. Indeed, while one object of selection is 
to reduce numbers, by far the larger object is to purify the 
ancestry, to the end that inheritance from all the ancestors shall 
be alike, so that the "pull of the race" shall not be different 
from the transmission of the immediate parent. This being so, 
selectiojt according to vacillating standards is no selection at all, 
and he who returns from each state fair or exposition with 7iezv 
rather than improved standards cannot hope to meet the highest 
success as a breeder or contribute real excellence to the breed 
he has chosen. 

SECTION II — HISTORICAL KNOWLEDGE OF THE BREED 

NECESSARY 

This is almost self-evident, and yet the number of breeders 
who do not possess it, and the readiness with which large money 
is invested and plans made which will require a lifetime to carry 
out, — all with the most' meager knowledge of the breed that 
is chosen, ■ — show how lightly this matter rests in the minds of 
many otherwise intelligent and cautious business men. 

These men proceed as if the material they were to work with 
were new material, ready to be molded for the first time into 



58o PRACTICAL PROBLEMS 

any desired form, while in truth it is very old material, with 
which many men have worked before, — sometimes for profit, 
often for amusement merely. 

And the breed has inherited the results of all these experi- 
ments, both bad and good, so that this material is in some 
respects the better and in some the worse for what others have 
tried to do with it. The most ordinary business sense and the 
commonest biological principles indicate that before the breeder 
begins serious operations he should know all that can be known 
of the breed or the variety he proposes to work with. In no 
other way can he make intelligent selection. 

A few crude examples will suffice to illustrate. Many breeders 
of English strains of cattle will not only destroy a white calf, 
but will consider its appearance an evidence of impurity of blood, 
not knowing that these breeds in general have descended from 
the wild white cattle of Great Britain. It is only recently that 
white has been restored to favor as a good Shorthorn color. 

The Berkshire swine are the result of a cross of the large 
English hog with the small, thin-haired, plum-colored Neapolitan, 
and more than one Berkshire herd has been ruined by selecting 
for breeding purposes the plump, cjuick-maturing, fine-haired, 
and most attractive pigs. 

A famous breeder of Kentucky was remarkably successful 
with Shorthorns, yet in his efforts to secure a high head and a low 
brisket he forgot the natural wild type, and speedily his breeding 
came to be known by its sloping rump and " split quarters." 

The breeder should know the peculiarities of his blood. The 
first information needed by the prospective breeder is a good 
knowledge of the inherent faults of the breed. He needs to 
know, for example, that the Berkshires are naturally deficient in 
the hams, and the Poland-Chinas in the shoulders ; that the 
Duroc Jerseys are uneven in type, and the Chester Whites a 
bit coarse in the bone. He needs to realize that the Jersey is 
sometimes extremely delicate ; that rriany of the Holstein-Frie- 
sians are rough, and that the breed is preeminently short-tailed, 
— hence the provision in the scale of points that the bone of 
the tail should reach the hock, which was but rarely the case in 
the foundation stock of the breed. 



SELECTION 581 

The breeder of Shorthorns should know in advance that it is 
a breed not of one type, but of many types, of varying degrees 
of excellence. He who expects to breed Herefords should know 
at once that the breed is one of two types, so distinct as to be 
almost dimorphic. The Angus breeder should not be surprised 
at some failures, or at a red specimen, nor the Galloway breeder 
at considerable roughness, or at the occasional appearance, with- 
out warning, of more or less white. 

Breeders of the Percheron should know that, of all modern 
breeds, this retains the most of the Arabian infusion due to the 
crusades, and that until recently he was a small not a heavy 
horse, hence his " bone " is to be carefully looked after. 

These and a mass of other breed peculiarities, both good and 
bad, should be fully in the mind of the breeder. Of course most 
of the advocates of any breed will stoutly resent the slightest 
implication of faults in their favorites, yet the fact remains that 
the really able and successful breeders know very well that they 
must be constantly upon their guard against certain happenings 
which may be called " faults " or " peculiarities " according to 
the definition of terms. 

SECTION III — GENERAL PRINCIPLES INVOLVED IN 
SELECTION 

When the breeder determines which individuals shall and 
which shall not reproduce, he must do it with all the intelligence 
possible, and with a full knowledge of all that is involved in his 
decision, which is most far-reaching and irrevocable in its con- 
sequences. It is the purpose here to outline some of the prin- 
cipal considerations that should be in mind when these decisions 
are made. 

The purpose of selection. Primarily the purpose of selection 
is to reduce numbers, or to influence type (whichever way we 
please to put it), but in the last analysis it is to prevent the 
birth of unwelcome individuals not suited to the purposes of 
man ; and by as much as the breeder is able to forecast off- 
spring, by so much is he able to surround himself with good and 
serviceable individuals without resorting to wholesale slaughter 



582 PRACTICAL PROBLEMS 

after birth, with its attendant losses. In all theory we would 
prevent the birth of unprofitable individuals, and we succeed 
nearly in proportion as we are skillful in selection. 

Selection results in absolute increase in quality, not merely in 
an elevation of the average by eliminating the lower values. 
We have been told that selection results only in raising the 
average by cutting off the lower values, but that the upper 
values are not influenced thereby. This is clearly an error, as 
will be seen by a reference to any systematic breeding experi- 
ments and especially to the tables giving the results of selecting 
corn for high or low protein or high or low oil.^ Here it is seen 
that, in the progress of selection, by the use of successively 
increasing standards, nciv and higher values constantly appeared. 
Not only that, but the principle is still operative after ten years 
of selection, and the coefficient of variability is not, in most cases, 
groiving less? In general it may be said that the result of 
systematic selection is to shift the type but not greatly to 
reduce variability, and when applied to a number of characters 
at the same time it very clearly and very rapidly defines the 
type of the strain or breed. 

In breeding the beet for sugar, the cow for milk, the horse 
for speed, or any animal or plant for any definite quality, there 
is every reason for believing that we have succeeded in pro- 
ducing a higher order of excellence than ever arose spontaneously 
in the race while in a state of nature ; that is to say, we have 
done more than to raise the average, we have elevated the 
Jipper limits. 

The upper limits of improvement. Manifestly this increase of 
cjuality cannot go on indefinitely. We cannot breed the horse 
to be as large as the elephant ; or, if we could, there will be an 
upper limit somewhere. What will set these limits is an interest- 
ing question. In some cases, no doubt, the limit would be fixed 
by purely mechanical principles,'^ in others by physiological 
restrictions, such as the size of the heart and the labor of 

1 See pages 494 and 496. 

2 Ibid. 

3 For example, there is a mechanical limit to the length of leg, or to the size 
of udder. 



SELECTION 583 

circulating the blood ; but apparently we have not yet, in any 
line, approached a limit so high that variation is not abundantly 
able to present still higher values. How long this may go on is 
a question both of scientific and of utilitarian interest, but it will 
be remembered that variation is supposed not to be reducible 
below some 85 or 89 per cent of its original amount.^ 

Selection for definite purposes often against valuable qualities, 
especially fertility ,2 vigor, and longevity. So intent are we upon 
securing some coveted character, as early maturity, size, milking 
or feeding quality, that we overlook other less visible but none 
the less essential qualities. This is best seen among our meat- 
producing animals. For example, it is the heavy-fieshed, early- 
maturing sow pig that finds her way to the prize ring and ulti- 
mately to the fashionable breeding pen. Now this is not the 
most prolific type of swine, and under this policy of selection, 
primarily for flesh and fat, it is not surprising that, of all our 
animals, those bred for meat production are lowest in fertility. 
We know of no fundamental reason why it must be so ; it simply 
is so because fertility has been so generally neglected in the 
exclusive standards and methods of selection employed. 

"Fertility," "vigor," and "longevity" are all relative terms. 
All animals and plants have some degree of vigor, and nearly 
all are able to reproduce, at least to some extent. The evils on 
this score arise not from the non-breeder, or the individual that 
succumbs in early life, but from those individuals which, though 
not entirely wanting, are yet deficient in those fundamental 
({ualities that are of necessity correlated with propagation of a 
vigorous, lasting, and prosperous race. It is the " shy breeder" 
that comes to nothing, and that is the root of many of the evils 
of the breeding herd. 

The relative values of prolific and of shy breeders may be 
brought out by comparing three cows, for example, one of which 
will produce two calves before she stops breeding, another four, 
and another six. After five generations the fertile female 
descendants of each would be as follows, assuming that one half 

1 Pearson, Grammar of Science, p. 483. 

2 The word " fertility " is used in preference to " fecundity " because the latter 
term refers especially to females. 



584 



PRACTICAL PROBLEMS 



the calves are males and one half females, and that all descendants 
arc prolific in the same proportion as the originals. 

Number of Living and Producing Females at the End of 

Various Generations, from Cows of Different 

Degrees of Fertility 







Tota l 
Calves 


Females 


Cow No. 


First 
Generation 


Second 
Generation 


Third 
Generation 


Fourth 
Generation 


Fiftli 
Generation 


I 
2 

3 


4 
6 


I 
2 

3 


I 
4 
9 


I 

8 

27 


I 

16 
Si 


I 
32 

243 





It is easy to see that no matter what the individual excellence 
of cow No. I and her descendants, they could never build up a 
herd. Their rate of reproduction is so low as only to keep good 
the original number. Careful search will discover a surprising 
number of females of this class in the herds of otherwise suc- 
cessful stockmen, — useless from any standpoint except the 
show ring. 

On the other hand, cow No. 2 and her descendants produce 
at a rate that will not only keep their numbers good but will 
admit of selection, and this is the case to a greater extent with 
No. 3, whose descendants in the fifth generation would be no 
fewer than 243 as compared with 32 for No. 2 and i for No. i. 
It is easy to see that one such cow as No. 3 in a herd of 20 
like No. I would in a few years, by very breeding powers, 
dominate the herd, at the same time affording generous num- 
bers for selection, whereas the descendants of No. i would 
afford no opportunity whatever for selection. It is clear to the 
most casual student that iv/icn our standards are decidedly 
against tJie highest fertility they are dangerous, if not futal, to 
the race. 

Need of comparatively large numbers in breeding operations. 
Obviously, comparatively large numbers are necessary in order to 
provide selection with material sufficient for securing uniformity 



SELECTION 585 

in type. Enthusiastic amateurs have often attempted to maintain 
a "small herd of exceptional excellence." Such attempts have 
always failed, and must fail, for the reason that such a herd 
affords too little material for selection, and therefore the impos- 
sibility of maintaining its type is a bar not only to progress, but 
even to the bare maintenance of the initial excellence. Suppose, 
for example, that a small herd of exceptional animals be brought 
together, — say, three cows and a bull, the choice from many 
of the best herds. What are the mathematical probabilities of 
their being able to reproduce their own number of equal excel- 
lence before the original herd disappears .'' It is very slight 
indeed, unless one of the number proves to be a phenomenal 
individual breeder, which, in truth, occasionally happens. 

Value of the exceptional breeder. The more the matter is 
studied the more it will be found that tJie excellence of any herd 
or of any breed is sustained and advanced, not by the general 
mass, but by a few exceptional, not to say phenomenal, breeders. 

The trotting blood of to-day owes its high development to a 
very few foundation animals, coming to us through Hamble- 
tonian 10, and sustained and developed by an insignificantly 
small percentage of the general mass of stallions.^ 

The excellence of the Shorthorn is maintained in the same 
way, and it is not too much to say that in all probability there 
are never living at any one time in any breed more than a score 
or so of animals that produce anything like a real and positive 
advance in the breed, ^ — " The line of descent runs not through 
their veins." 

The exceptional breeder not necessarily the exceptional indi- 
vidual. Neither Hambletonian 10 nor Geo. Wilkes was the 
best trotter in the breed ; indeed, the highest performers have 
contributed little. They were the offputs, but accidentally, or 
of necessity, they were not of the main line of descent. In the 
corn-breeding experiments already cited, the ear to which the 
present high-protein stock all traces was not one of the originally 
highest protein ears. The great sires and the great dams that 

1 See chapter on " Heredity," table of the l>ig Ten, p. 555. 

2 This number is too high. The Shorthorn breed probably never saw twenty 
such bulls as Champion of England. 



586 PRACTICAL PROBLEMS 

have contributed most to their breeds have often been incon- 
spicuous as individuals and, unfortunately, often have been dead 
long before their real service to the breed was known and 
recognized. 

Need of the actual breeding test. So valuable is the excep- 
tional breeder, and so impossible is it to know him (or her) in 
advance by the ordinary methods of judgment, that only the 
actual breeding test is reliable. The only safe method is to 
select the herd of females of high fertility and uniformly excel- 
lent breeding record, and then, knowing the female side by long 
and intimate experience,^ select the sire for his performance 
record in getting young. 

The tests should first be made with a few well-known, and 
therefore fairly aged, females. Too mncJi catinot be said against 
the practice of putting a 7iew young sire at once into full service 
in the he?'d, no matter what his individuality or his pedigree. 
However promising, he must be subjected to the actual test, 
and after having proved his breeding powers with known females 
he should be used to the utmost as lojig as he zvill breed siiccess- 
fully, and not discarded because of loss of bloom, decline in 
form, or even for the acquirement of an evil disposition. It is 
from the proved patriarchs and from the grandmothers of the 
herd that real excellence will come, and the real value of proved 
breeders, male or female, is beyond computation.^ 

Install the successor early. It is never too early to seek a new 
head to an established herd. Proved sires are seldom for sale, 
and the only recourse for the breeder is to prove his own ; 
indeed, what he needs is a sire that will produce well with his 
females. 

It takes much time and often many trials to find a worthy 
successor to the head of the herd. Putting it off too long, and 
a feeling of fancied security, are the two causes of leaving a 

1 A complete breeding record should be kept of each female separately. See 
chapter on " Animal Breeding." 

^ The author has a mass of data collected from hundreds of breeders, from 
which it appears that young bulls are commonly preferred because they are cheaper, 
because their period of service is longer, and because they are more manageable. 
It appears too that when a " test " is made it is commonly not upon old and known 
cows, but upon heifers. 



SELECTION 587 

herd without a head, and of the enforced evil practice of using 
an untried sire. 

Comparative value of male and female. In the matter of pre- 
potency, as we have ah'eady seen, neither parent has any partic- 
ular advantage over the other. But this refers to a single 
offspring, and is only a part of the question. The real differ- 
ence is one of numbers. Among animals the sire may produce 
perhaps a hundred in a season, while the dam is limited to one 
individual or at most (among hogs) to two litters. The trotting 
records show that certain sires produced literally hundreds of off- 
spring in the list, but the greatest record ever made by any mare 
was that of Green Mountain Maid, who produced nine living foals. 

For purely mathematical reasons, therefore, the female is of 
vastly less consequence in herd or breed improvement, — indeed, 
wherever polygamous mating occurs. It is here a question of 
numbers and opportunity. As regards these, the upper limit of 
the male is very high and of the female very low, which fact 
teaches the necessity of extreme care in the selection of the 
sire, not so much for biological as for numerical reasons. The 
single female is, therefore, comparatively iiisignificaitt. Unless 
she be one of the few phenomenal breeders her individual power 
for good is exceedingly low, and the readiness of many buyers 
to pay extreme prices for females, especially of cattle, is wholly 
unaccountable. 

The sire more than half the herd. It has become a proverb 
that the sire is half the herd. He is far more than that. He 
is half of the first generation, three quarters of the next, seven 
eighths of the third, and so on until, if judicious selection be main- 
tained for a fezv generations, the character of the herd zvill be 
fixed by the sire alone. This being true, the folly of maintaining 
a sire with but two or three high-class females is evident ; he 
should have larger opportunity. All this means that, as a begin- 
ning, numbers are of more consequence relatively than quality 
on the side of the dam, and that if the breeder must choose 
between the two it is better to put a given amount of money 
into a good number of plain females than into a smaller number 
of high quality, but that in all cases the sire should have quality 
and plenty of it, because of the principle here stated. 



5.SS I'KACI'ICAI, l'ROBl,KMS 

Size in the dam ; quality in the sire. In many lines of brccd- 
\\v^, size in Ihe sire is considered by many breeders as of first 
imporlanee. This is against reason and biolof^ical i)rinci|)les. 
We need in the sire all Ihe desirable ehai'acteis ])ossible, and 
these are niosl readily found in animals of iiiciiiniii, not extreme, 
size. It is comparatively easy to j;et size alone, and this ean be 
<;()tten on the side of the dam. The herd must depend for uni- 
formity largely u|)on tin; sire, and he should be heed as much 
as possibK- from the recjuirc-nu-nl ol si/e.' 

Natural selection always at work. Natural selection is always 
at work in Ik-M and llo( k and herd. Of this we may be well 
assured. No matter what we desire to accomplish, our success 
or our failure will turn, in the last analysis, upon the fitness of 
the product to live and to reproduce amid the conditions by 
whic-h it must be surrounded. 

Some of the best things amoni; both plants and animals are 
weak or com])arati\ely unprolilic. Natural selection is decidedly 
against their survival, no matter how valuable they may be to 
us. Lac-k of constitution or vigor is easily seen, but lack of 
breeding powers is not so easily detected, and here is where 
the greatest amount of trouble arises. 

We have already seen that in nature the population that is 
lyoni into llic ivorhi is f^rof^oilioiud (ucordiit}^- to relative ftrti/ity, 
while the population thai is permitted to roiiaiii is conditioned 
u])on relative powers to icsist adverse conditions and to lit into 
the conditions of file. 

This same relation obtains in our herds, with this difference, 
that 7(V, with our selection, decide arbitrarily what shall live. 
That is right and according to economic necessity, — only in 
doing so we must not assume that all indixiduals and types are 
e(|ually fertile and ecjually able to ])ropagate themselves. 

It may be in certain instances that in order to secuie what 
ue desire we shall of necessity proceed temporarily with some 

1 \ mimifcst cMcplidn lo (his general piiiuiplc is in llic Ijiccding of draft 
lioisi's fioni farm maics. Ilere .si/.e is an object inn on llie dam's side, l)esidcs 
l)eiiij; diflieull In gel. Weiglit is Ihe < ///<;/"desideral iini just now (il will iiol always 
l)e so) in draft horse bleeding, and under //('.ivv// i in utuslantes il niiisl be sought 
csjiecially in the sire. 



SELECTION 589 

handic-ap as to fertility, and i)crlKii)s as to vi^or, in vvhicli rase 
these two essential (|ualities must be borne in mind and tin- 
delieieney remedied in future selections. The breeder is never 
to forj^el that natural selection is at work side by side, or per- 
haps oi'cr, his best endeavors. In nature the prevailing;' type is 
a kind of resultant of the hi^diesl fertility and the best " Hi." 
It is not different in our herds. The type which //(^ /■///;•<■///)' appears 
in our herds will be decitled not only by our selections but by 
the relative fertility and vii^or of everything; |)resent. 

Examples are not wantin,i;' in which herds, and even whole 
families, have f^one down because of this une(|ual battle aj^ainst 
the i)ersistent inlluence of natural selection, 'ihe most notable 
instance is the " Duke and Duchess" family amoni; Shorthorns, 
— most excellent iiulixiduals and true to type, but not sufficitMitly 
prolific to maintain themselves. So they went down and out, — 
submerged under the inevitable deciee of natural selection that 
the unprolific shall die. The writer does not believe that this 
most excellent family need haxe been lost to the breed had tin; 
breeders of the day been sulliciently alive to the situation.' 

This resjionse to ineciuality in natural fertility of different 
strains is technically known as "frenetic selection," and it is 
everywhere at work. It must be reckoned with in some foini. 

Physiological selection. Certain individuals are sterile; to each 
other. It is a dil'licult) seldon) encountered, but whi-n it does 
occur it constitutes an effective bar to those particular blood 
combinations, howexcr desirable. Because it is limited to ])airs 
of individuals, its interference is occasional rather lh;ui com- 
mon; yet, when encoimtered, it should be reco^ni/.ed, and time 
and expense avoided in attemi)ts to overcome it. 

Influence of age. Statistics show that a surprisingly large 
proportion of sires are so young as to be clearly immature. The 
effect of this has been much discussed, and the general o|)inion 
seems to be that breeding fiom immature animals is bad. 

1 This family was always known If) Ix; " sliy breeders. " The wiilcr well 
remembers heariiij^ breeders say, " I low fortunate that this is so, else prices would 
not he iiiiiiii/ii/iie(/." Ilapjjy would it have been could these same breeders iiave 
read their doom in time to save their pockets ! They had ample warning, had they 
known how to read the handwriting on the wall. 



590 PRACTICAL PROBLEMS 

In truth we have httle exact information on which to rely, but 
the writer seriously questions the correctness of this conclusion 
from tJic standpoint of the offspring. That breeding at an imma- 
ture age checks the growth of females is next to certain, but it is 
also true that the heifer will make a better milker and a more cer- 
tain breeder if bred before maturity and before functions other 
than milk production hav'e become the prevailing habit of life. 

That the progeny of immature animals is necessarily faulty 
is doubtful. In nature everywhere reproduction bcgijis before 
maturity, and in man at least it has been shown that the length 
of life of first children is, on the average, four years more than 
that of the latest born. 

Considerations already advanced in connection with testing 
breeders necessitate the breeding at a comparatively advanced 
age, and all things point to the conclusion that in practice breed- 
ing may begin early and continue as long as possible. Merely to 
gain time, if for no other reason, early breeding is to be advocated. 

Blemishes and accidental injuries. Notwithstanding popular 
opinion, the breeding animal is none the worse for accidental 
injury ; that is, so far as his or her breeding value is concerned. 
The question is not whether the mare is spavined, but what kind 
of a hock had she nat?i?'a/ly, and had she sufificient occasion to 
be spavined. It is easy to make a bad showing and to say bitter 
things about the practice of breeding injured animals, but the 
evidence on inheritance all shows that injuries as such are not 
transmitted. This should not free the mind from the obligation 
to judge accurately as to whether the part was naturally perfect 
or naturally defective. 

Difficulties in selection increase rapidly with the number of 
points on which selection is to be based. This purely mathematical 
consideration seems not to arrest the attention of breeders as it 
should. If we select for one point only we get ahead rapidly. 
That has been the advantage of the trotter. Speed was the only 
requirement, and while it involved many subordinate conditions, 
such as a perfect body, vigor, endurance, mental courage, and 
determination, yet no other requirement has been added. Color, 
size, style, action, conformation, — all have been disregarded 
for the one object, speed. 



SKLF.CTION 591 

Over against this the Dutch Belted Cattle, for example, have 
an absolute color requirement. Every cow must first have a 
white belt around her body. This certainly has nothing to do 
with her milking abilities, yet the absurd specification has gone 
into the very name of the breed, — a fact that will keep the 
breed materially behind its competitors in matters for which we 
breed cows.^ 

The more clearly to show the extent of the handicap of 
striving after many points in selection, let the student work it 
out mathematically. If but one point is required, and it can be 
satisfied, say in one tenth of the individuals, then the chances 
of getting it are one in ten, and one tenth of the breed is 
available. 

Now to this let us add a second requirement that can be 
found in but one third of the individuals. The probability of 
finding these txvo points in the same individual will then become 
not -^-^ or \, but -^-^ X \, or -^-^, and only about three animals 
in one hundred will meet the requirements. 

Need of reducing the requirements to the utility basis. In 
fashionable animal breeding we have so multiplied our points 
that we are no longer able to find any very large proportion of 
them in any one individual, and we are often obliged to tolerate 
positive evils in order to get the requirements even within the 
limits of the herd. This is virtually mixed breeding. 

What is needed is a return to first principles, — to select a 
very limited niimbe}- of the points most important from the 
utility standpoint. Let these be so few and so pronounced that 
they may all be found in evejy individual of the breeding herd. 
Then later, as 7inmbers multiply, other points can be added, a 
few at a time, upon a practically pure ancestry ^o far as previous 
points are concerned. " This one thing I do " should be worn in 
the hat of every breeder. A little courage here would soon 
work wonders ; but " points " have become so multiplied in some 
of our breeds that all possibility of finding any individuals that 
possess them all has long ago been passed, leaving us in a 

' The writer hesitates to use as forceful language as the above regarding any 
breed, because in general all breeds are good, but this is a step so clearly adverse 
to live-stock interests that no language is too strong in condemnation. 



592 



PRACTICAL PROBLEMS 



wellnigh hopeless jumble, with pedigrees meaning next to nothing 
so far as definite information goes. 

Importance of pedigree. Enough has been shown to point 
clearly to the fact that the simply "good individual" is worth- 
less as a breeder.^ He must be the product of a good ancestry, 
and moreover of the right kind of good ancestry. It is not 
enough that the animal or plant is not mixed in its blood. We 
ought to know, and our pedigrees ought to show, what were the 
special characters of the ancestors. There is yet so much 
variability in all our breeds that a simple guaranty of non- 
infusion of outside blood is not enough. Something positive is 
needed, and great success awaits the breed whose breeders will 
take a few points at a time and establish a double registry, one of 
which shall be a record of tJic degree in w/iich the indi-oidual 
actually possessed the domiiiant characters of the breed. If the 
"advanced registry" of some of the dairy breeds can be safe- 
guarded against abuses, and then be used as a basis for selection, 
it will be of untold benefit to the breeds and to the country at 
large. 

SECTION IV — RATIONAL SELECTION 

When and to what extent to depart from safe general prin- 
ciples on account of economic or other considerations is a matter 
calling for the most discriminating judgment. 

Fancy points. It is perfectly easy to show that if the breeder 
succeeds in fixing really useful characters he will have his hands 
more than full ; and yet, despite all this, fashion constantly sets 
certain fancy points, and insists upon their observance. The 
trouble is not only that most of these fancy points have little or 
no utility, but also that, like any other caprice of fashion, they 
are likely to change frequently and without warning, whereas 
all considerations of selection require constancy and simplicity. 

What, then, shall the breeder do } He is bent upon building 
up a herd of the highest practical value, and he has carefully 
weighed the relative value of all utilitarian characters. All of a 

1 The regression table clearly shows that an inferior individual from a good 
ancestry is in every way superior to a perfect individual from a heterogeneous 
ancestry. Both are evils, but of the two the latter is by far the worse. 



SELECTION 593 

sudden, however, fashion thrusts to the front some absurd 
requirement, and insists that it be met, or the stock will remain 
unsold. The breeder is in business not for amusement, but for 
gain, as well as for satisfaction. He must sell his product, or 
very soon go out of business. He cannot afford to go on pro- 
ducing what nobody will buy, and he is often brought face to 
face with the alternative, — financial ruin, or the destruction of 
the herd from the standpoint of the best breeding. 

For example, a few years ago all really good horsemen were 
amazed at the demands of the market for exceedingly high 
knee and hock action. It was a gait not only awkward to look 
upon (except to men who were not horsemen), but it was exceed- 
ingly hard on the horse, and entirely impractical except for 
park purposes. Yet this was the demand, for the time, on the 
part of the buyers who spent their money freely, and it was 
met by the breeders, for such demands are powerful influences 
in setting standards. 

Yet no one knew better than these same breeders that the 
fashion was a passing one. To what extent, then, should studs 
be disturbed, and standards regarding free, easy, and useful 
action be upset by a passing whim ? Requirements of fashion 
such as these — and they are many and frequent in the breed- 
ing business — call for all the judgment of the breeder, and all 
his knowledge and skill in meeting issues and in freeing himself 
and his herd or stud quickly from the evil consequences of ill- 
advised standards. 

The whole situation presents a case of steering between diffi- 
culties and accepting the least of two evils, — injury to the 
breeding stock upon the one hand and loss of sales upon the 
other, and it rivals international diplomacy in the fineness of 
distinctions to be observed. 

There are two ways of meeting situations of this kind with a 
minimum of danger. One is to meet the demand as far as pos- 
sible by training instead of breeding ; ^ the other is to introduce 
whatever is to be introduced at once in tJic person of the sire, 

1 This plan was actually used to its limits in the days of high gaits, when by 
proper shoeing, driving over rough ground, etc., much was "trained into" the 
roadster being fitted for market. 



594 



PRAcriCAi. pr()f,ij<:ms 



hoping the craze may pass before the old stock of females shall 
pass away. If it does not, then at all hazards some remnants 
at least must be j)rescrve(l ])in-e and unalloyed as a nucleus 
against the day when the pendulum will swing back to the 
normal, or perhaps to the other extreme. 

Breeders' fads. The above has reference to requirements 
imposed by the buyer. But the fact is, breeders themselves 
have multiplied their natural difficulties enormously and use- 
lessly by fads of their own invention, the tyranny of which is 
even worse than that exercised by the alien buyer. Against all 
this the strongest protest is far too weak. 

Why, for example, should a few curly hairs on the back of a 
hog disqualify him as a breeder ? Why are cows and bulls 
selected by the size or shape of the escutcheon ? Why must 
a Jersey have a black tongue .'' Why must the tail bone of a 
Holstein-Friesian cow reach to the hock .? Why did the Shorthorn 
breeders twenty-five years ago carefully kill every roan or white 
calf, and so yield themselves to the color craze that for a decade 
or more the breed made progress backward ? Why such frantic 
horror at the " seventeens," ^ requiring that a book be written 
blacklisting literally thousands of the best animals of the breed .? 

Absurd standards of this character should be resisted to the 
utmost by every reputable breeder and by every real friend of 
the breed, whether arising ignorantly or from a malicious desire 
to narrow the range of possible sales, to discredit the animals 
of competitors, or to destroy their herds. The writer is well 
aware that breeders as a c/ass are second to none, either in 
intelligence or in honor. He is aware, too, that many of these 
foolish requirements or objections, like the " querl " on the pig, 
get started no one knows how, and gain strength by repetition ; 
but the wholesale destruction of reputations, and even of herds 
and fortunes, by the war on the "seventeens" is convincing proof 
that individuals, even in this honorable company, are not above 
the most dastardly methods of reducing competition. Individ- 
uals of this sort are not bona fide breeders ; they are commercial 
jiirates who use pedigreed live stock as material for speculation. 
They have added nothing to the excellence of any breed, or to 

^ Reference is here made to the Shorthorn importation of 1817. 



SELECTION 



595 



the honor of breeders, who, as a class, are the soul of honor, and 
would no more falsify a pedigree than they would rob a bank. 

Such methods must be met, and breeders' fads generally 
shoultl receive their everlasting quietus within the confines of 
our breeders' associations. If this may be, then the individual 
will be reasonably safe ; if not, then he must take his chances 
with the rest, but against this insidious enemy of all good breed- 
ing his voice and his pen should be instant and active, — this in 
the interest not only of his own business but of the breed he loves. 

Fashionable pedigrees. All agree, and the law of ancestral 
heredity proves, that the ancestry back of the individual is 
extremely potent ; yet this potency largely resides in the near-by 
members, and to see a breeder poring over a pedigree running- 
ten or twelve generations back to an "approved " individual on 
the female side, and then gravely nodding approbation of a 
" good foundation," — this is indeed both humorous and pathetic. 

According to the law of ancestral heredity as stated by Galton 
and fully noted in a previous chapter, each generation and each 
iiuiividiial oi the various generations has an influence represented 
by the following fractions, waiving all questions of prepotency : 

Relative iNTENsrrv of Blood Lines and Approximately Relative 

Influence of Different Generations and Individuals 

FOR Ten Generations Backward 



Generation 


Number of 


Influence of Genera- 


Influence of Each 


Backward 


Ancestors 


tion—Per Cent 


Inuividual — Per Cent 


I 


2 


50.00 


25.00 


2 


4 


25.00 


6.25 


3 


8 


12.5 


i-56-f- 


4 


i6 


6.25 


0.39 + 


5 


y- 


3-1-5 


0. 10 — 


6 


64 


1.5625 


0.024 -f 


7 


128 


0.78125 


0.006 + 


8 


256 


0.390625 


0.00 1 + 


9 


512 


0.1953125 


0.0004 — 


10 


1024 


0.09765625 


0.000 1 — 


Total 


2046 


99.90234375 1 





1 This will be 100 if carried to infinity. 



596 PRACTICAL PROBLEMS 

By this we see that the individual inherits from no less than 
2046 individuals within ten generations of ancestry, and that, 
on the average, characters possessed by a single individual of 
the tenth generation back have an influence amounting to not 
over one ten thousandth of one per cent of the total heritage, 
representing a probability of about one in a million — certain to 
be heard from but of little consequence as 2i foujidation. 

We must remember that besides the " foundation " there are 
1023 other ancestors of the tenth generation, and some 1022 
intervening ancestors, each more powerful by far than the 
so-called foundation. Six generations back the influence is but 
1.5 per cent for the sixty-four individuals involved, or about 
^-Q of one per cent for each. This is an amount of influence 
which for practical purposes may be considered as a negligible 
quantity, and it is for this reason that in many lines the dictum 
has gone out, " The sixth cross is pure," this meaning that 
nearly 99 per cent is covered by the " top." We have seen 
already that this agrees perfectly with mathematical theory. 

The so-called foundation is therefore not a foundation, but 
only a beginning, and it is the top, and not the bottom, that gives 
character to the pedigree. 

This is not intended to disparage purity of pedigree even to 
the tenth generation and beyond, but it is intended as a protest 
against the blind following of certain pedigrees because of the 
" foundation." 

Nor is it to be construed as a criticism directed against breed- 
ing along approved lines ; far from it ; but it is a plea for the 
careful study and rational valuation of pedigrees. 

What deceives the breeder is the fact that the " short form 
pedigree," as it is often presented, runs only on the feina/e side, so 
that, of the 2046 ancestors of the first ten generations, only eight 
or ten females and their sires would appear — the other 2026 
not being noted. They exist, however, and their influence is to 
be reckoned with. Of course it is true that in close breeding 
the same individual appears many times in a pedigree, and thus 
his or her influence is multiplied ; but the point here made is 
that a single individual ten or even six generations back counts 
for little so far as its personal influence is concerned. 



SELECTION 597 

Rational standards. In the interest of rational breeding, let 
ideals be made up of essentials, — a few strong lines, which, 
like the bold strokes of a great painting, make the picture stand 
strongly out, unimpaired by a multitude of unimportant details. 

Summary. The whole purpose of selection is to modify the 
type to better suit our purposes, to prevent so far as possible 
the production of undesirable individuals, and to reduce the 
population as near as may be to those that are useful in the 
highest attainable degree. 

If the last item is to be accomplished, then the "pull" of 
the ancestry must be in line with the immediate parentage, which 
means that there must be a constant, not a fluctuating, standard 
of selection. 

The probability of finding all desirable qualities in a single 
individual reduces rapidly as the number of characters multiplies. 
It is represented by the product of the chances of each, and if 
many characters are involved it becomes practically impossible 
to find them all in the same individual. This leads inevitably 
to heterogeneous breeding within the breed, and to confusion of 
ancestry with respect to separate characters. 

The practical way to " fix " a large number of characters is to 
do it with one or two at a time, or at most a few at a time, 
adding others as it becomes comparatively easy to secure them 
all in the same individual. Common sense dictates that we 
should begin with the most important from the utility stand- 
point. In all breeds there are too many animals that do not 
conform to type, even approximately, and most standards of 
selection call for too many points. 

Fads and fashion, confined for the most part to minor matters, 
are the bane of good breeding. They must be reckoned with for 
economic reasons ; but in the effort to meet market demands it 
is sometimes difficult to avoid the fixing of decidedly objection- 
able characters. 

It is the "top," rather than the "foundation," that gives 
character to the pedigree, and in all cases the individual should 
conform to the standard of selection. This calls for a degree of 
detailed information about individuals for at least five or six 
generations back, which we do not ordinarily possess, and which 



598 PRACTICAL PROBLEMS 

the records do not undertake to supply, but which breed histories 
should afford for the enlightenment of young breeders and to 
the end that unfortunate combinations may not be unwittingly 
made. The student will recall the difference between brothers, 
which shows the need for selection even within the pedigree. 

When a family becomes famous it is bred with less ability and 
care than before, whereas it is deserving of greater and more 
careful attention. But conditions are against it : the individuals 
have a high commercial value, and everything goes at a strong 
price, indifferent and bad as well as good. As long as men 
will pay for breeding, regardless of quality, breeders are likely 
to sell everything that will find a buyer. A large number of 
breeders have reported to the writer that they sell lOO per cent 
of their animals for breeding purposes. Under conditions such 
as these all selection is practically abandoned, and we should not 
expect longer to maintain excellence. Thus it is that the very 
success of a popular strain is likely to prove its undoing. 

This state of affairs sufficiently accounts for most disasters that 
have overtaken fashionable families in the past, and we are not 
yet warranted in assuming that a favorite strain is bound quickly 
to wear out or otherwise come to an end, making it necessary 
that we should be forever effecting new combinations. Indeed, 
there is the best of ground for the confident belief that if a 
tithe of the labor were bestowed upon the preservation of a use- 
ful strain that was expended to originate it we might have it with 
us indefinitely, to the infinite good of the breed and the lasting 
service of man. It is not a continually recurring strain of new 
creations that is most needed, but rather well-protected and 
solidly bred lines of long-established excellence and unquestioned 
ancestry. Here, in the opinion of the writer, lies the field for 
future effort of American breeders. 



CHAPTER XVII 

SYSTEMS OF BREEDING 

Of the various possible systems of breeding some are better 
adapted to one purpose, others to another; some again are 
pecuHarly adapted to animals, and others to plants. The practi- 
cal breeder should first of all have a clear idea of what he is 
trying to do, and then an accurate knowledge of the various 
systems that can be employed to achieve his purpose. 

SECTION I — PURPOSES IN BREEDING 

The general principle that should decide the system to be 
chosen and adhered to depends upon the answer to the following 
question : Is the pin-pose of the breeding to improve the Jierd, — 
that is, the home stock of the farmer ; is it to improve the breed 
or variety as a ivJiole ; or is it to originate new varieties 1 

The answer to this question should determine the system of 
breeding to be adopted. These purposes are separate and dis- 
tinct. The first is herd improvement, the acknowledged object 
of which is to build up the home stock until it approaches in 
excellence the approved breeds or strains. This is purely com- 
mercial and purely selfish, in the best sense of the terms, in that 
the breeder is not operating for the good of anybody or anything 
but himself and his own, and is not aiming to outdo anybody- 
else ; his purpose is, rather, to secure for himself the improve- 
ment that others have originated. It is the cheapest and easiest 
of all forms of breeding and productive of the most rapid results. 

The second purpose is, on the other hand, chiefly the improve- 
ment of a recognized breed or variety, — an improvement in- 
tended to endow the race more richly than ever before. This is 
the very highest style of finished breeding, and calls for the most 
intelligent and expensive methods, because in this case the 
breeder is a leader, not a follower and an imitator. 

599 



6oo PRACTICAL PROBLEMS 

The third purpose in breeding is not to improve anything, 
but to secure something entirely new, different from, and pre- 
sumably better than, any previously existing strains. In carrying 
out this purpose the breeder proceeds upon the assumption that 
our varieties are too few ; that gaps exist which may be filled up ; 
and that it is better to produce something new than to de- 
pend upon improving the old. This is the most ambitious of all 
forms of breeding, and appeals to creative genius rather than 
to conservative business instincts, which incline to improve- 
ment of existing races rather than to the production of new ones. 
Naturally it is most common in plant breeding, in which numbers 
are not so serious a matter, and in which breeding operations are 
less expensive. 

As has been remarked, these three purposes in breeding are 
entirely distinct. These distinctions should be clearly in the 
mind of the student when studying systems of breeding, and the 
breeder himself must be in no sense uncertain as to which one 
is really in his mind when he begins his breeding operations. 
If his purpose is to improve his own, let him frankly admit it 
to himself and proceed accordingly, leaving high prices and 
hazardous enterprises to others. If, on the other hand, he 
hopes to do something distinctive for his breed, and is satisfied 
that he has the money and the patience to do it, then again his 
purpose is clear cut and his methods are well indicated. 

All breeding expensive except herd improvement. ^ All forms 
of breeding are costly whenever the purpose is to prodiiee some- 
thing better than ever before. If the purpose is only to multi- 
ply excellence, then it is comparatively cheap, but the original 
production of excellence, which is breeding in the highest 
sense of the term, is relatively expensive, because so few 
individuals, plant or animal, excel either their predecessors or 
their contemporaries, and so few of these can propagate their 
own excellence. 

With these considerations in mind it is worth while to get a 
clear idea of the different systems of breeding available for the 
various purposes. 

1 " Herd improvement " is an expression used in reference to tlie home stock, 
whether plant or animal. 




6oi 



6o2 



PRACTICAL PROBLEMS 



SECTION II — GRADING 

By " grading " is meant the mating of a common or relatively 
unimproved parent with one that is more highly improved, that 
is, a "pure bred." The mating might be made either way, but 
in practice the male is taken for the pure-bred parent for 
economic reasons. One pure-bred bull with a herd of twenty 
cows can give all the calves in the herd a pure-bred sire (that is, 
make them half bloods), whereas if the making of half bloods 
were attempted in the other way it would require twenty pure- 
bred individuals, and the crop of calves would have no more 
improvement ; besides which, the improvement made would be 
not in one but in twenty lines, each with its shade of difference. 

Expressed in terms of money, it is possible to give all the 
calves in a herd a pure-bred sire — that is, make them all half 
bloods — at a total cost of approximately two dollars per calf, 
assuming, of course, a reasonable number of cows in the herd 
and a bull at a moderate price but good enough for grading. If 
the making of half-blood calves were accomplished in the other 
way, however, — that is, by providing the pure-bred parent on the 
dam's side, — it would cost, at the same relative rate, close to 
forty dollars as a minimum. This shows the necessarily extreme 
cost of pure breds as compared with grades. 

Disappearance of Unimproved Blood by the Continuous Use 
OF Pure-Bred Sires 





SiRKS 


Dams 


Offspring 


Generations 


Per Cent of 


Per Cent of 


Per Cent of 


Per Cent of Un- 




Purity 


Purity 


Purity 


improved 


I 


lOO 


O 


50 (i) 


50 (D 


2 


lOO 


5° 


75 (1) 


^5 (1) 


3 


lOO 


75 


87-5 (1) 


1^-5 (I) 


4 


lOO 


87.5 


93-75 (li) 


6-35 (tV) 


5 


lOO 


93-75 


96.87 (II) 


3-1 3 + (5V) 


6 


100 


96.87 


98-44 (If) 


1-5+ (sV) 



Improvement by grading is of course limited to herd improve- 
ment. It adds nothing to the breed, but it distributes breed 




6o^ 



6o4 PRACTICAL PR(JBLEMS 

excellence rapidly and with extreme certainty. Such a sire is 
almost surely prepotent over the dams, whatever they may be, 
and the mathematics of mating shows that if the practice is 
continued for six generations, but one and a half per cent of the 
original unimproved blood will remain, as is shown in the table 
at the bottom of page 602. 

By this we see that the unimproved blood soon becomes insig- 
nificant and rapidly disappears. This is why it is that in the 
early days of a breed the sixth or seventh cross is declared 
eligible to record. 

It should be noted that if any one of these generations be 
bred with itself (grades with grades) no progress is made. Thus 
individuals of the second generation are one fourth unim- 
proved, and, bred to a generation of their own kind, they will 
still remain one fourth unimproved. By the same principle, 
half bloods bred to half bloods will produce half bloods indefi- 
nitely. The effects of grading cease the moment we discontinue 
the pure-bred sire. 

Abuse of grading. The chief drawback in grading is that it is 
likely not to be followed up. The breeder is almost certain to 
choose some promising half or three-quarter blood for a sire 
because he ''looks as good" as a pure bred, and then by the 
law of ancestral heredity all improvement stops except the little 
that can be accomplished by the slow process of selection. 

Advantages of grading. For economic purposes grades may be 
equal to pure breds, but they are ivortJiless for breeding purposes ; 
this is the plain conclusion of what is well known of the prin- 
ciples of breeding. Grading is cheap. By the use of a single 
individual it secures at once something more than half of the 
total excellence of the breed, and if followed up it will secure in 
time, through sires dAona, practically all of it. 

This is the system of breeding to be recommended to the 
great mass of stockmen, and if it could be generally adopted 
"Axvdi followed up it would add millions to American agriculture. 
Every stockman knows that the great bulk of the best cattle in 
the markets are high-grade Shorthorns and Herefords. The 
accompanying figures surely show that the less-known Angus 
and its close relative, the Galloway, are equally successful for 



SYSTEMS OF BREEDING 



605 



grading purposes. The failure to make the most of grading is 
the largest single mistake of American farmers and the most 
conclusive evidence of shortsighted business policy on the part 
both of the general farmer and of the breeder of pure-bred stock. 
Breeders of pure-bred stock largely to blame. When breeders 
themselves stop trying to set up amateurs, who have little money 
and less experience, with small herds of two or three females, 
then the longest step will have been taken toward reform in this 




Fig. 48. Seven-eights blood Angus steers, si.x months old. — Property of Hon. A. 
P. Grout, Winchester, Illinois 



particular. These pitifully inadequate efforts at breeding are 
foredoomed to failure, after which the unfortunate farmer, smart- 
ing under the punishment he suffered by reason of his spasm of 
enthusiasm for better stock, forthwith and forever curses not 
only the breed that " let him down," but blooded stock generally 
and breeders in particular. 

The breeder's business is the production of sires. The profes- 
sional breeder is a producer of sires, and he should sell males, 
not females. He should take the amateur kindly into his confi- 
dence and explain that while he himself is in the business for 
profit, and his animals are for sale, yet he fully realizes that 



6o6 PRACTICAL PROBLEMS 

grading is the breeding for beginners. He can easily show the 
novice that if he will keep his old females, or, if not, get plenty 
of such as are easily available, he can have as many grades 
within a year as he can provide females now, and that speedily 
he will own a herd that for all practical purposes except breed- 
ing will be as good as anybody's, all at a cost of only two or 
three dollars per calf, and correspondingly less or more for other 
animals. Such a course will demonstrate at once the excellence 
of the breed, and make friends, not enemies, of the man and 
his neighbors. 

The burden is upon the breeders and owners of pure-bred 
flocks and herds to lead in a crusade for grading. They need 
the market for their excess of males, and if this market were 
fully developed, and the mass of stockmen fully alive to the 
advantages of grading, this market alone would absorb at good 
prices all the male output from our breeding herds, — a consum- 
mation they stand sorely in need of attaining. 

The female output of our breeding herds should be used, first, 
to reenforce the home herds, and after that to supply deficiencies 
in other reputable herds. Any further surplus animals should go 
to the open market, except in some rare cases in which they are 
needed for the real founding of new herds. 

The main difficulty is that the breeders, as a rule, are too 
intent upon selling females and setting up a multitude of little 
breeders in a small business ; whereas they should be not only 
intent, but persistent, in selling males for grading purposes. 
This is their great market, their natural outlet, and its exploita- 
tion is their opportunity. The author has replies from hundreds 
of breeders on this point. A large share of them profess to ex- 
pend as much effort to sell females as to sell males, and a few 
even more. Associations have much to do along this line. 

Begin animal breeding by grading. Grading is the safest begin- 
ning, even for the prospective breeder of pure-bred stock. Not 
only is it cheap and safe, but it will bring out clear and strong in 
the grades the main breed points, and a few generations of grades 
from low to high will spread out before the eyes of the breeder 
such a panorama of breed characters as he would not see in 
years of pure breeding on a small scale ; indeed, there is no 




6o7 



6o8 PRACTICAL PROBLEMS 

quicker, cheaper, or more thorough way of becoming acquainted 
with a breed than through its grades. 

Disadvantage of grading. The only disadvantage that can be 
mentioned is this, — that the first results are so eminently satis- 
factory that some promising grade is likely to be selected as a 
sire, regardless of the law of ancestral heredity, whereupon all 
further improvement stops. This is so likely to be the case that 
it may be said in general that the very success of grading is the 
greatest guaranty of its failure. 

SECTION III — CROSSING OR HYBRIDIZING 

Almost the exact opposite of grading, crossing combines 
ancestral lines of two distinct races, breeds, or varieties, in the 
hope either of securing a blend or else of getting a fortuitous • 
combination of characters. 

This form of breeding is adapted only to the production of 
new strains, in which it excels. Of course it so mixes blood lines 
as to effectually destroy the influence of the ancestry and all 
meaning and value of pedigree. Its hope is in starting a new 
strain, which may perchance breed pure. 

The operation of Mendel's law teaches how small is this 
chance. If this law always held with all races and characters, 
it would of course be impossible to secure permanent strains 
by crossing, but the fact remains that permanent hybrids Jiave 
f?rq?ient/y been secured by this method, especially among plants, 
which is a noteworthy fact in breeding. 

Advantages of crossing. Notwithstanding the operation of 
Mendel's law as a general principle, crossing is a fruitful source 
of new strains. Hybridization is better adapted to plants than 
to animals because of the need of vigorous selection afterward 
and, therefore, of relatively large numbers. It was a favorite 
method of plant improvement twenty years ago, but it has fallen 
largely into disuse because of the inconstancy of Mendel's 
middle term (the 50 per cent apparoit hybrids) and because as 
good or better results can often be secured by selection alone, 
xvitJiont destruction of the pedigree and tlic influence of the 
ancestry. 



SYSTEMS OF BREEDING 609 

Disadvantages of crossing (hybridizing). The difficulty of 
securing a blend out of a violent cross, or indeed anything 
that will breed pure, and the great mass of long-continued and 
disappointing reversions experienced, have turned the attention 
largely away from this system of breeding, to one which, if less 
spectacular, is eminently safer, and, so far as we now know, 
fully as fruitful of results. 

It is the opinion of the writer, however, that as we learn by 
experience it will be found that certain races of plants will lend 
themselves well to this means of producing new varieties, and 
that the old-time enthusiasm for hybridization will return in 
these exceptional cases. 

Crossing is a powerful means of inducing variability, — indeed, 
it is the most powerful method known to breeders. It is alto- 
gether too fruitful of variants to be manageable in animal breed- 
ing, and only sheer necessity, after all other methods have failed, 
would warrant its trial among these slow-breeding races. 

If animals are to be hybridized it can probably best be 
accomplished by combining, not two races simply, but three or 
more, leaving the one nearest that which is wanted untouched 
until a fairly favorable cross between two others has been secured. 
Then the pure form, if bred with the cross, might be influenced 
thereby, but would of course remain prepotent. Such a plan of 
action aims rather at the modification of a breed than at the 
creation of a new one. 

Hybrids often sterile. All degrees of productivity are found 
in hybrids, from extreme fertility to absolute sterility. Some 
crosses are more fertile than either parent. Such a cross would 
be made readily in nature. Others are absolutely or nearly sterile. 
It is safe to assume that about all the possible fertile hybrids 
were long ago produced in nature, and either went down under 
natural selection, or became good species before they came into 
our hands. However, modified strains may yet be hybridized, 
and sterile hybrids may often be propagated asexually. 

The classic hybrid is the mule or hinny, the cross between the 
horse and the ass, and is nearly always sterile. The lion and the 
tiger mate freely, in captivity at least, but the mating is in most 
cases fruitless. Even here, however, hybrids have been born. 



6io PRACTICAL PROBLEMS 

The reciprocal cross. Strange as it may at first appear, the 
two possible crosses by interchange of the sexes often, though 
not always, differ substantially. It is said that the common 
mule more nearly resembles the ass, and the hinny the horse. 
Other instances have been noted, and the point has been urged 
that reciprocal crosses are in general dissimilar. It is the 
■writer's opinion that the rule applies only to those particular 
characters in which the one parent (either male or female) is 
prepotent over the other because of sex. However, statistical 
evidence on reciprocal crosses is almost totally lacking. 

The whole subject of hybridization seems at present to 
promise little of interest to animal breeders beyond the produc- 
tion of the common mule, but if we may place a shrewd guess, 
it will yet be found a fruitful source of new varieties in certain 
races of plants, in which propagation is so easily effected by 
budding, grafting, or other form of asexual multiplication, thus 
avoiding the effects of Mendel's law in a way quite impossible 
with animals. 

SECTION IV — LINE BREEDING 

By " line breeding " is meant the restriction of selection and 
mating to the individuals of a single line of descent. The pur- 
pose of this system of breeding is real breed improvement, — 
to get the best that can be gotten out of the race, and better 
than ever before if possible. 

Experience has shown that if the purpose be breed improve- 
ment, or even herd improvement carried to its limits, it is not 
enough to confine selection to the limits of the breed. All 
breeds are exceedingly variable, and real results aiming at any- 
thing more than mere multiplication can follow only closely 
drawn lines within the breed, — breeding in line, or line breeding. 

Line breeding excludes everything outside the approved and 
chosen line of breeding. It not only combines animals very 
similar in their characters, but it narrows the pedigree to few 
and closely related lines of descent. This "purifies" the pedi- 
gree rapidly and gives the ancestry the largest possible oppor- 
tunity. The system is eminently conservative. It discourages 



SYSTEMS OF BREEDING 



6ii 



variability, and rapidly reduces it lo a minimum. Moreover, 
whatever \'ariations do occur will be /// line i^ntli the proviinetit 
characters of the chosen 
branch of the breed. 

Advantages of line 
breeding. The nature of 
results secured by this 
system can almost cer- 
tainly be predicted ; and 
when they do appear, and 
improvement is at hand, 
it is backed up by the 
most powerful hereditary 
influence obtainable, be- 
cause of the simplicity 
and strength of the an- 
cestry, which, if the selection has been good, all " pulls " in the 
same direction. The records of all breeds will show the pro- 
nounced results that have followed judicious line breeding. A 
volume could be filled with pictures of famous animals so pro- 




FiG. 50. Baron Duke 63d, a line-bred Berkshire. 
Property of A. J. Lovejoy, Rosco, Illinois. 
Figures 51 and 52 show get of this boar 




Fig. 51. Line-bred Berkshire pigs. Get of Baron Duke 63d 



duced. Those shown are of swine, for the reason that the pig is 
popularly supposed to be the most sensitive to close breeding. 

Disadvantages of line breeding. The chief danger in line 
breeding is that the breeder will select by pedigree, abandoning 



6l 2 



PRACTICAL PROBLEMS 



real individual selection. A line -bred pedigree is valuable or 
dangerous in exact proportion as the individuals have been kept 
up to grade. It will not replace selection, but, on the contrary, 
calls for the most discriminating care tvithin the line. 

If the breeder selects by paper, and not in the yards, and a 
few generations of inferior animals creep in, then line breeding 
will consign the whole bunch to the limbos quicker and more 
certainly than will any other known system of breeding, — a 




Fig. 52. Liue-bit'd yciiling lieikshiics. Get of IJaion Duke 63d 



fate that has overtaken more than one line that unfortunately 
became prematurely fashionable. 

Line breeding the best system for improvement. No other 
system of breeding has ever secured the results that line breed- 
ing has secured, and if the present state of knowledge is reason- 
ably sound, no other system will ever be so powerful in getting 
the most possible out of a given breed or variety, especially of 
animals, and this with the greatest certainty as we go along. 
The only requirement is, not to abandon individnal selection. A 
pedigree is not a crutch on which incompetence can lean ; it is 
a guaranty of blood lines, — a field inside of which breeding 
operations and selection may with confidence be confined. 

The word " confined " is used advisedly, for, after line breed- 
ing has been practiced for a few generations, the ancestry 
becomes a kind of pure breed of its own, — a breed within a 
breed, so to speak, — and any attempt to introduce blood from 



SYSTEMS OF BREEDING 613 

other lines is likely to be followed by the pains and penalties of 
hybridization ; for a departure from line breeding is a kind of 
crossing in a small degree, and so rapidly do blood lines become 
intensified that line-bred animals assume all the attributes of 
distinct strains, as they in truth are, and they will be likely to 
behave as such ever after. 

In saying that line-bred animals tend to behave like pure 
strains, and that their progeny from union with other strains 
behave like hybrids, it is not meant that such unions should 
never be made, or that such behavior is as persistent as with 
real crosses. In truth, many lines are so stubborn as never to 
blend with others afterward (behaving like the most strongly 
established races), but, on the other hand, most of them will 
yield to well-directed and persistent effort ; that is to say, a 
line-bred herd can be modified, and in time made to assume the 
characters of another family, but the process is attended with a 
struggle and not a few failures. It has been fashionable at 
times to decry line breeding, but the fact remains that a few 
generations of good breeding soon bring the herd and its career 
to a point where line breeding must be practiced or a worse 
alternative must be accepted, for with well-selected strains all 
outbreeding is mixed breeding. 

SECTION V — INBREEDING 

Line breeding carried to its limits involves the breeding 
together of individuals closely related. When it involves the 
breeding together of sire and offspring or of dam and offspring 
or of brother and sister, it becomes inbreeding, or " breeding in 
and in." It is line breeding carried to its limits, and of course 
possesses all the advantages and disadvantages of that form of 
breeding carried to their utmost attainable degree. 

Forms of inbreeding. Three forms of inbreeding are possible 
among animals, namely : 

I. Breeding the sire upon his daughter, giving rise to off- 
spring three fourths of whose blood lines are those of the sire, 
— a practice which, if followed up, soon results in offspring with 
but one line of ancestry, thus practically eliminating the blood 



6 14 PRACTICAL PROBLEMS 

of the clam. This form of breeding is practiced when it is de- 
sired to secure all that is possible of the blood of the sire. 

2. Breeding the dam to her own son or sons successively, 
thus increasing the blood lines of the female side. This form is 
practiced when it is the dam's blood lines that are to be 
preserved and condensed. Both systems are neces.sarily limited 
to the lifetime of the individuals involved. Either system can 
of course be approximated by the use of granddaughter or 
grandson, which would by common consent be called inbreed- 
ing, but relationship more remote would generally be regarded 
merely as line breeding. 

3. Breeding together of brother and sister, — a form of in- 
breeding which preserves the blood lines from both sire and dam 
in equal proportions. It is inferior to either of the others as a 
means of strengthening previously existing blood lines, but it is 
freely employed when the combination has proved exceptionally 
successful, virtually establishing a new type. It has all the dangers 
of the other two, and in a larger degree, because we have prac- 
tically no acquaintance with the new combination, whereas in 
strengthening the proportion of one line of ancestry over another, 
whether it be that of the sire or that of the dam, we are dealing 
with previously existing blood lines known to be harmonious. 

Among plants there are two forms of inbreeding, namely : 

1. That in which the fertilization is with pollen from another 
flower on the same plant. 

2. That in which fertilization is by pollen of the same flower. 
This, being hermaphroditic, is the closest imaginable inbreeding, 
and exceeds anything that is possible with animals. 

Advantages of inbreeding. Nobody claims advantages in in- 
breeding per se, but it is the acme of line breeding, and when 
superior individuals are at hand it is the most powerful method 
known of making the most of their excellence. It is the method 
by which the highest possible percentage of the blood of an 
exceptional individual or of a particularly fortunate " nick " can 
be preserv'ed, fused into and ultimately made to characterize an 
entire line of descent on both sides. 

If persisted in, the outside blood disappears by the same law 
that governs grading, and the pedigree is speedily enriched to 



sYsri';Ms oi' i'.ki.iodinc; 015 

an almost; unlimited cxtcnl liy tin- Mood ol ;i sin^^-Jc ;iiiiiii;il, 
in practice, f^ciierally that ol llif site ll is a niellKxl iioi so 
miK li of originating excellence as ol making llic most ol it when 
it does a|)|)ear, and it is not too hum li to say thai a larjM- |)io 
portion of th(; really f^aeat siics have been sti(»ii;^,ly inbred. 

An inbri:d animal is ol (oiirse enorinoiisly pnpoicnl over 
everything else. Its hall ol iIk- antcstry, biin!-, Iai|;cly ol id< n 
tical blood, is almost (criain to dominate 1 he ollsprin;-, lnbi<cd 
in^ is, therefore, re( o^ni/.<-f| ;i', the si longest ol all bifi-fimj,/, 
givinf^ rise to the simplest of pedij^^rees, - an advanlaj.;e (|iii( kly 
recognized when we recall the law of ancestral heredity. In this 
respect it is all that line breeding.; is and mote. 

A second advantage is that siiccessfiil asHficiations of ( har- 
acters are preserver! inU*ct and not shatterefl by the infusion of 
new strains. If the breeder were dealing with but a single < hai 
acter he could readily find its efjual, and there would be liitle 
need for inbreeding; but even if breeding lor but a single utili 
tarian character, he always has at least two others, vigor and 
fertility, which must be included in selection. In practice h<; lian 
many more, and a single inrlividual that r ontains all or most of 
them in a high degrei; is a veritable bonanza; naturally the 
temptation is to make the most of an oj^porturniy whir h i-, none 
too frequent in the breeding business. 

AU things consid<;refl, no other known method ol bleeding 
equals this for intensifying blood lines, doubling up existing 
combinations, and making the most of exceptional individuals 
or of unusually valuable strains. 

Disadvantages of inbrfcedinj.^. Clearly, however, this is not a 
gun to "hit the bear and miss the calf." This " doiil^lirig uf; " 
process, this intensifying of characters, increasing their prospects 
from pfj«sibility to probability and afterward to certainty, w/orkn 
exactly the same for one character as for another ; // fifft'ds all 
characters of the individuab involued, had as well as f/xxl ; and 
so it is that this methrxl, which i« applicable to both plant and 
animal breeding, and which aims at making the greatest use 
possible of our most valuable possessions, has U:en followed 
alike by the most strikingly successful result* and by the m<^;^t 
stupendous disasters that ever overtrK;k the breeding business. 



6l6 PRACTICAL PROBLEMS 

Plenty of examples of successes can be instanced, and every 
breeder is familiar with them. The failures have been many, 
but they are not to be counted here, for the blood lines in- 
volved are long since extinct. 

Special dangers from inbreeding. Tradition everywhere has it 
that inbreeding, if long continued, is practically certain to end 
in loss of vigor and of fertility, and plenty of instances are given 
to '■'■ prove " it. 

Now a rational consideration of the principles of transmission 
has already led us to expect that bad characters as well as good 
will be intensified. We could not expect so powerful a method 
to work only to our advantage and to grant immunity from dis- 
advantage in all cases. 

What we want to know is whether, in respect to trouble, 
we are to look out for likelihood or for certainty ; whether disas- 
ter is inevitable, or only extremely probable. This question has 
been much befogged by certain catchy statements such as, 
" Nature abhors incestuous breeding," all of which confuse an 
ethical and social question with the biological one in which only 
we are interested. 

Inbreeding not necessarily disastrous. Our attention is con- 
stantly called to " nature's provisions for preventing inbreeding," 
and to " ingenious devices for inducing cross pollination by 
insect aid " ; but we are not reminded that many species of 
plants are self-pollinated, nor is our attention called to the many 
famous sires that were strongly inbred, nor to the fact that in 
nature among gregarious animals the head of the herd is sire of 
practically all the young (so long as he remains master), many of 
of whom are thus doubly his. Nor do we have it called to our 
attention that, while corn seems peculiarly sensitive to inbreed- 
ing, wheat is self-fertilizing to the closest possible degree, and 
that it is perhaps the most vigorous, prolific, and all-round cos- 
mopolitan success among our domestic plants. 

Lack of vigor and low fertility the two most common defects. 
If what has been said and shown has any meaning, it is that any 
character can be bred up or down, strengthened or weakened 
by this method of breeding. Why then its evil reputation with 
respect to vigor and fertility 1 Is there some inherent injury 



SYSTEMS OF BREEDING 617 

from close breeding, or is it merely that vigor and fertility are 
commonly defective characters and frequently find themselves 
on the losing side ? Undoubtedly it is the latter. There are 
cases enough of the greatest vigor and fertility of inbred indi- 
viduals, and of family lines and even of whole species, to set 
aside all fear of inevitable injury from close breeding, but a 
little study will convince us that there is lurking weakness and 
infertility everywhere. It is said that one third of our children 
die in infancy. A large proportion of animals and an apparently 
larger proportion of plants are relatively weak and easily suc- 
cumb to disease or to the encroachments of their neighbors. 

Few individuals are fully fertile, — that is, free and regular 
breeders, — and fewer yet are both fertile and vigorous. Short- 
comings in these two respects may be called the distinguishing 
defects of both plants and animals under domestication. In 
nature they constitute the chief points of attack of natural selec- 
tion, but in domesticated animals and plants we commonly select 
for other points, even color, trusting to luck for vigor and fertility. 
Is it any wonder that these lurking evils have crept upon us 
until they often constitute an insurmountable bar to inbreeding, 
and have invaded even our most carefully outbred herds } 

As inbreeding is the supreme test of a race, so it is of a char- 
acter ; if a character suffers by inbreeding it is a sign of natural 
defectiveness and should be accepted as such, and not laid up 
as an additional instance and a weapon with which to abuse a 
system with a history of laudable achievement in the past and 
rich with possibilities for the future. 

When we select for vigor and fertility we shall hear less of the 
evils of inbreeding. In the meantime we shall hear most about 
it where vitality and fertility are naturally lowest. Both are 
cardinal requisites, — one for life, the other for reproduction, — 
and both must be possessed in a high degree by any individual 
or family line that is to figure much in descent. 

Noting, then, the remarkable instances of successful inbreed- 
ing, as well as its unexampled capacity for trouble, we arrive 
at the conclusion that the disaster from inbreeding is probable, 
but not inevitable. With that much gained, it is worth while to 
examine further into this disputed territory. 



6i8 PRACTICAL PROBLEMS 

Darwin's experiments.^ Fortunately so far as plants are con- 
cerned we are not without some accurate data tending to show 
the actual effect of inbreeding upon the two most important 
characters here under discussion, — namely, vigor and fertility, 
— and for a great variety of species. The experiments are too 
extensive to fully discuss even by abstract, covering as they do 
some fifty-seven species, belonging to fifty-two genera ; ^ but 
their results may be briefly stated. 

The careful study of these experiments shows the following 
facts: (i) that in gejieral, and without a doubt, crossed forms 
(both they and their offspring) are, on the average, much more 
fertile and far more vigorous than are the self-fertilized ; (2) /;;// 
that this is not trne of all species, nor is it true of all individuals, 
even within those species most sensitive to inbreeding. 

Thus, of the 83 species tested for height, 26, or nearly one 
third, were either within 5 per cent of the height of their cross- 
bred companions, or else exceeded them in height. Of these 26 
cases, however, he concludes that 14 were actually inferior, — if 
not in height, at least in other respects, — leaving 12, or one 
seventh of all, that quite clearly were not inferior when inbred, 
and in some cases were decidedly the better for it.^ Concluding, 
Darwin remarks : 

Therefore if we exclude the species which are approximately equal, there 
are thirty-seven species in which the mean of the mean heights of the 

^ Charles Darwin, Cross and Self Fertilization in the Vegetable Kingdom, 
p. 482 [D. Appleton & Company]. It is unfortunate that we do not possess 
equally full and exact data as to inbreeding among animals, but at this point our 
knowledge is limited to general results and to individual experiences. The marked 
success of close breeding and even inbreeding in our herds is attributed to the 
special skill of a "master breeder." That this is not the full explanation is shown 
by the experience of the United States Bureau of Animal Industry. Some years 
ago it became necessary to remove the stock of guinea pigs to new quarters a 
considerable distance away. A severe storm was encountered en route and only a 
few pigs were saved. From these few, and with no infusion of outside blood, the 
present stock is descended, and the writer is credibly informed that the stock is 
exceptionally vigorous and fertile. 

2 The student desiring the data upon the effects of cross- or self-fertilization in 
general should read chap, vii, pp. 238-284, of Darwin's Cross and Self Fertiliza- 
tion, etc. ; for data concerning the effect upon seed production he should read 
chap, ix, pp. 312-355 ; and for data concerning other effects, chap, viii, pp. 285-31 1 ; 
for detailed reports of different species see chaps, ii-vi, especially ii. 

3 Darwin, Cross and Self Fertilization, etc., pp. 279-283. 



SYSTEMS OF BREEDING 619 

crossed plants exceeds that of the self- fertilized by 22 per cent, whereas 
there are only five species in which the mean of the mean heights of the 
self-fertilized plants exceeds that of the crossed, and this only by 9 per cent.^ 

The writer again calls attention to the fact that while averages 
are of prime consequence in commercial transactions, they do 
not decide principles of breeding, and it is extremely suggestive 
that even five species were decidedly more vigorous when inbred. 
It determines definitely that there is nothing inherently and 
necessarily evil in inbreeding, per se, for if such were the case it 
would make itself evident in every instance. 

Speaking of the fertility of self-fertilized flowers, Darwin says,^ 
" Their fertility ranges from zero to fertility equaling that of the 
crossed flowers ; and of this fact no explanation can be offered." 
Not only was this true, but the self-fertilized forms were some- 
times actually more fertile than the crossed.'^ 

This mystery, for which "no explanation can be offered," is 
largely cleared up by our modern knowledge of heredity, as 
is shown by what follows. 

The total effects of inbreeding. All characters, both good and 
bad, exist in various degrees in different individuals. The prob- 
lem in breeding is to secure the strongest combinations of desir- 
able characters, and it is easy to show that this is accomplished 
by inbreeding. Not only that, but it is also easy to show that 
the same methods will secure the loivest attainable intensity, — 
a consummation desirable with unwelcome characters, and good 
to know about as a general possibility. 

Take, for example, three intensities of any single character, 
disregarding for the moment all questions of correlation. Let 
these three intensities be represented by 3, 2, and i, respec- 
tively, 2 being the mean. 

If, now, we exclude inbreeding, we find three unions possible, 
— namely, 3 + 2, 3+1, and 2 + i ; but if we resort to inbreed- 
ing, we make also the matings 3-4-3,2 + 2, i + i. Which unions 
are richest in results ? In which have blood lines been most 
intensified .'* 

1 Darwin, Cross and Self Fertilization, etc., p. 283. 

^ Ibid. p. 326. 

3 Ibid. pp. 322-325. 



620 PRACTICAL PROBLEMS 

Relative Effect of Outbreeding and of Inbreeding 





Mating 


Mid-Pakents 


Offspring 


Outbreeding . . . . ^ 




3 + 2 

3+ I 

2 + I 


3 + 2 

3 + ' 

2 

2 + I 
2 


= 2-5 

= 2 

= 1-5 


Inbreeding 


- 


3 + 3 

2 + 2 
I + I 


3 + 3 

2 

2 + 2 


= 3 


2 
I + I 


= I 



From this we see that both systems produce the same mcan^ 
but that inbreeding produces the wider extremes (3 and i). 
Hence the greatest 7'ange of possibiUties lies with inbreeding, so 
far as immediate parentage alone is concerned, and the advantage 
is of course still greater in the ancestry farther back. 

Again, the table shows what will happen on the average under 
the law of regression, but in exceptional cases the law of pro- 
gression will apply, from which we see that the advantage for 
inbreeding is still greater ; in other words, it is by inbreeding 
that the highest and the lowest attainable results can be pro- 
duced, and this is because no other system can produce so high 
(or low) a mid-parent, or in the end so " pure " an ancestry. All 
of this indicates a principle that is abundantly powerful for 
intensifying good characters or for breeding out evil ones. The 
fact that it is thus powerful argues against its use with any but 
superior individuals. Furthermore, inbreeding is a supreme test 
of excellence, and if a family line or an individual endures it, its 
characters are above reproach. 

Not all inbred individuals inferior to the cross-bred, even in 
species especially sensitive to inbreeding. One of Darwin's most 
extensive series of experiments was carried on with the common 



SYSTEMS OF BREP:i)ING 



621 



morning-glory {Ipoincea purpurea)} This species was bred both 
crossed and self-fertiUzed for ten generations. In every genera- 
tion the crossed forms were larger than the self-fertilized, the 
average being as 100 is to yy. Not only that, but they were 
clearly the more productive. The species, therefore, is one that 
on the whole is extremely sensitive to inbreeding. Let us, how- 
ever, analyze the details of the experiment and observe how it 
fares with individual plants. 

Darwin's plan was to put the cross and the inbred seeds into 
moist sand at the same time, and then to pair them off in the 
order of their germination. That is, the first cross-bred seed up 
would be paired with the first inbred seed up as a competitor,^ 
the two being planted on opposite sides of the same pot ; the 
second would be paired with the second, the third with the third, 
and so on.^ 

The following table, reporting the first generation, shows how 
the results appeared at first. 



Heights of Cross-Bred and In- 
bred Stock, — First Generation * 



The average of these six 
pairs is 86 inches for the 
cross-bred and 65.6 for the 
self-fertilized, an initial differ- 
ence of approximately 20 
inches, which on the whole 
did not greatly change during 
the ten generations of the ex- 
periment. 

It will be noted that in this 
table every inbred plant is 
inferior to its cross-bred mate ; 
not only that, but no inbred 
individual of the series is as good as the poorest cross-bred 
reported. 

1 Reported in full in Darwin's Cross and Self Fertilization, etc., chap, ii, 
pp. 28-62. 

2 If, however, a seed germinated long before a corresponding mate appeared, 
it was thrown away, the aim being to mate seedlings that germinated exactly 
together, giving an even start. 

3 Uarwin, Cross and Self P^ertilization, etc., pp. ii, 12. 
* Ibid. p. 29. 



Number of 
Pot 


Crossed 


Inbred 


I 

In pairs 


87.5 in. 

87.5 
89 


69 in. 
66 

73 


In pairs 


S8 in. 

87 


68.5 in. 
60.5 


3 
Plants crowded 


77 in. 


57 in- 



622 



PRACriCAL PROBLEMS 





Number of 
Pot 


Crossed 


Inbred 


I 


84 in. 
47 


80 in. 
44-5 


2 


83 in. 
59 


73-5 in- 
51-5 


3 


82 in. 

65-5 
68 


56.5 in. 

63 

52 



On this point compare the facts reported in the following 
table for the fourth generation.^ 

Here again each inbred plant is inferior to its particular mate, 
but only tJiree of the cross-breds equaled the best inbred plant 

of the series (80 inches), and 
all but one of the inbreds were 
more vigorous than the poor- 
est cross-bred. 

The same general fact is 
noticeable in the next (iifth) 
generation, though not quite 
so pronounced, except that in 
one case the inbred plant 
equaled its own mate. Evi- 
dently something was prepar- 
ing to happen. 

The appearance of ** Hero." In the next (sixth) generation 
there appeared a specially vigorous plant that overtopped its own 
competitor by half an inch and exceeded in height all but three 
of the series. Darwin named this plant " Hero," and remarks, 
" I was so much surprised at this fact that I resolved to ascertain 
whether this plant would transmit its powers of growth to its 
seedlings." 

Accordingly he fertilized a number of flowers of Hero with 
their own pollen, and planted the seedlings in competition with 
other inbred plants and with cross-bred as well. The two tables 
on the next page show how the descendants of Hero acquitted 
themselves. 

Here, then, out of a species sensitive to inbreeding, has arisen 
a plant that is strong, vigorous, and prolific, and its own inbred 
seedlings at once demonstrate their superiority not only to other 
inbred stock but also to their crossed competitors. As Darwin 
remarks,^ " Hero transmitted to its offspring a peculiar consti- 
tution adapted for self-fertilization"; and again, ^ "It appears, 
therefore, that Hero and its descendants have varied from the 
common type not only in acquiring great power of growth and 

1 Darwin, Cross and Self Fertilization, etc., p. 34. 
- Ibid. p. 50. 3 Ibid. 51. 



SYSTEMS OF BREEDING 



623 



NrMBER OF 


Chiluren 


Ordinary 


Pot 


OF Hero 


Inbred 




74 in- 


89.5 in. 


I 


60 


61 




55-25 


49 




92 in. 


82 in. 


2 


91-75 


56 




74-25 


38 



Cross-Fertilization Seedlings, 
— Seventh Generation of ■ 
Inbreeding 



increased fertility when sub- Offspring of Hero compared with 
jected to self-fertilization, but Ordinary Inbred Seedlings, — 
in not profiting from a cross Seventh Generation of 

with a distinct stock." Inbreeding 

Here is excellence through 
inbreeding under what may 
be called the hardest condi- 
tions, and it gives great en- 
couragement to the belief that 
if it is necessary to secure a 
strain of plant or animal that 
will prosper under inbreeding, 
that strain can be produced, 
and that its production is a 
question only of time, pa- 
tience, and expense. Hero will Offspring of Hero compared with 
undoubtedly be called a mu- 
tant in these days, but mutants 
are welcome. It must be borne 
in mind that Hero was not the 
only individual that demon- 
strated its superiority to cross- 
bred plants, but that this was 
a common circumstance 
throughout the experiments. 

Nor was the morning-glory 
the only case of the kind. Con- 
cerning his experiments with Mimulus (the monkey-flower, of no 
consequence to us except as showing a principle) he says : ^ 

In the third and fourth generations a tall variety, often alluded to, hav- 
ing large white flowers blotched with crimson, appeared amongst both the 
intercrossed and the self-fertilized plants. It prevailed in all the later self- 
fertilized generations, to the exclusion of every other variety, and trans- 
mitted its characters faithfully, but disappeared from the intercrossed 
plants. . . . The self-fertilized plants belonging to this variety were not only 
taller but more fertile than the intercrossed plants, though these latter in 
the earlier generations. were much taller and more fertile than the self- 
fertilized plants. 

1 Darwin, Cross and Self Fertilization, etc., p. 348. (Italics are mine.) 





Number of 
Pot 


Children 
OF Hero 


Cross-Bred 


I 


92 in. 


76.75 in. 


2 


87 
87-75 


89 in. 
86.75 





624 PRACTICAL PROBLEMS 

He adds/ " This variety sccjns to have beeonie specially adapted 
to profit in every 7vay by self-fertilization, although this proeess 
%vas so injurious to tJie parent plants dnri}ig the first four genera- 
tionsy Darwin's whole discussion of "highly self-fertile varie- 
ties " ^ is exceedingly valuable, not only because the author seems 
to consider the phenomena inexplicable, but more especially be- 
cause it establishes the fact that the closest inbreeding is not 
necessarily fatal. 

It should be noted, however, that these are exceptional in- 
stances, constituting no argument for indiscriminate inbreeding, 
but they do show that inbreeding is not necessarily headed 
straight for disaster and with a full head of steam. 

The breeding business deals not with averages but with pos- 
sibilities, and it is high time that the foolish horror of inbreed- 
ing be dissipated. If breeders had been as careful in certain 
other respects as they have been to avoid the slightest form of 
inbreeding, our flocks and herds would have progressed farther 
along the road of improvement. 

Experience in animal breeding. Any one who will take the 
trouble to study the pedigrees of famous families in almost any 
line of stock breeding will find that the foundation blood is 
most intensely bred. Indeed, the practical breeder working with 
material that is really of distinctive and peculiar merit comes 
soon to the point at which close breeding is inevitable, and he 
must face the issue sooner or later if he is to make any real use 
of his valuable creations. To breed them out is but to dissipate 
their excellence, and the only practical course is close breeding. 

Among cattle breeders this practice is too well known to 
need more than a passing mention, but the following extracts 
from personal letters recently received will show how it works 
upon the highly organized horse and the quick-breeding, heavy- 
fleshed swine. 

The veteran breeder of Arab horses, Randolph Huntington, 
of Rochester, New York, writes as follows : 

With me close breeding has proved a sure test for purity, and my best, 
most uniform results have been in breeding the dam to her son and to her 

1 Darwin, Cross and Self Fertilization, etc., p. 348. (Italics are mine.) 

2 Ibid. pp. 347-352- 



SYSTEMS OF BREEDING 625 

grandson, and then breeding the produce together, intensifying such breeding 
by going back to the grand-dam with the grandchildren, until I had a family. 

In this connection we do not forget that Messenger was 
three times inbred to Godolphin. 

The following from A. J. Lovejoy, of Roscoe, Illinois, gives 
his experience in breeding Berkshires. The quality of his stock 
is indicated by Figs. 50-52, and his reputation as a successful 
breeder is fairly won by many years of uniform success. He 
writes as follows : 

We are believers in quite close, even inbreeding. We find the greatest 
show animals are closely inbred. Sires to half-sisters is the most common 
form of close breeding, though cousins, nephews, and nieces, and even 
brothers and sisters are bred together with great success. It of course 
requires good judgment in mating animals that are particularly strong in 
individual merit. Should each have a bad defect in any way, we should 
expect that to be more manifest in the offspring than in the parents, and 
likewise the good points would be better; so if one mates equally good 
specimens the produce will be an improvement. There is no sire of any 
breed so prepotent as an inbred sire. When we get to the point where we 
feel the need of outside blood we mate an imported sow with our best boar, 
and from this litter we select a boar to use on the get of his own sire from 
other sows in the herd ; that is, we breed this boar on his own half-sisters. 

No man has bred Berkshires more successfully than N. H. 
Gentry, of Sedalia, Missouri, and no American breeder has been 
credited with a freer use of inbreeding. This veteran breeder 
writes as follows : 

My experience in inbreeding is that you do good, or fail, in proportion 
to the quality in the strain of blood ; that is, that you intensify what you 
have, let it be good or bad, let it be weak or strong in constitution. The 
theory advanced by the mass of people, to the effect that you degenerate 
size and weaken constitution, is all wrong unless the strain you are inbreed- 
ing lacks size as a rule, or lacks constitution. Animals that have plenty of 
size and a vigorous constitution can have these traits intensified as certainly 
as you can lessen the.se traits by inbreeding with strains lacking these 
essential traits. If 3'ou can intensify the one it seems to me as reasonable 
that you can the other ; so a man's success in inbreeding will depend upon 
what he has to inbreed with. Rightly and intelligently done I have never 
been able to detect any bad results whatever froni inbreeding. I inclose 
you my prize list of two World's Fairs, and it is especially true of my 
St. Louis winners that every animal was closely inbred. It has always 
been strange to me that most every person who has never given the subject 



626 PRACTICAL PROBLEMS 

any study whatever has a decided notion that inbreeding is dangerous. I 
presume our fathers tell us this simply because their fathers told them so 
and their grandfathers before them, and not one in many thousands has 
ever given the matter any trial or serious thought. Even with a trial it 
does not follow that every case will be a success, any more than the mating 
of animals not related will be a success in every case. The animals mated, 
whether kin or not, must be suited to produce good results ; that is, have 
no weakness in common, and as much good as possible. 

How to pfactice inbreeding. There are two situations espe- 
cially indicating this method of breeding. One is grading, in 
which it may ordinarily be practiced with impunity. The other 
arises in the very best herds when the breeder finds himself in 
possession of a small amount of very superior blood and is debat- 
ing how to handle it. If he insists upon breeding "out" he 
will lose it by dissipation. He has gone to the limits of line 
breeding ; what shall he do ? 

In a case of this kind the only course that promises anything 
is inbreeding. It puts the line to the severest possible test, of 
course, and the hazard is great, but the possible results are 
phenomenal. The really good breeder should always be ready 
to accept whatever hazard is involved. 

If it is to be done at all, the best way is to " {^o it and be 
done ivitJi it,'' and know the worst at once. Many breeders, 
fearing the consequences, go at the job gingerly, breeding 
a little more closely with each successive trial, as if to test the 
situation before making the bold and final stroke. This, if not 
successful, is to undermine the situation and accumulate num- 
bers of undesirable individuals ; in any event it consumes time 
that is valuable, for animals grow old quickly. 

The proper way is to make the boldest stroke at once, so that, 
if the worst happens, the original stock is left for other trials 
and the breeder is not possessed of a herd that is destroyed by 
unsuccessful, half-hearted attempts at inbreeding. 

SECTION VI — BREEDING FROM THE BEST 

This has reference to the practice of selecting and breeding 
from the best individuals but without reference to blood lines. 
It is probable, indeed it is certain, that in process of time 



SYSTEMS OF BREEDING 627 

exceedingly valuable races could be established in this way, 
especially on restricted areas and more particularly with field 
crops. 

But in actual practice the breeder following this method 
among animals succeeds in getting together a confused jumble, 
out of which nothing of note can be established. It is the 
practice followed by primitive races and by careless farmers, 
and as soon as some attention is paid to strains, to families, 
and to blood lines, it passes at once into some one of the other 
forms of breeding already discussed. 

In plant breeding the principle operates differently. Here 
numbers may be employed so extensively that after having 
chosen the stock we can literally hunt through thousands for 
the thing we want. This when found is, strictly speaking, a 
mutant, and having found it the plant breeder may proceed at 
once to multiply it by cuttings or to breed it pure, possibly by 
inbreeding, certainly with as little crossing as possible. This is 
the system followed by Luther Burbank, and by plant breeders 
generally who are looking for neza things, though it is often 
combined with crossing. 

Neither in animal nor in plant breeding, however, are we to 
expect much success except by regarding ancestral lines and 
living and working in full realization that the law of ancestral 
heredity is a fact. 

Summary. The system of breeding to be followed depends 
upon the purpose to be accomplished. Grading is the practical 
method of improving common stock and of quickly and cheaply 
getting acquainted with the essential characters of a breed. 

If the purpose is breed improvement through the perfection 
of family lines, then line breeding and even inbreeding will be 
the systems found most effective. 

If new types, new strains, and new creations generally are 
sought, two courses are open, — either to watch for accidental 
mutations, or to hasten their appearance by crossing, a form 
of breeding that produces individuals which are good, but which, 
under the common law of ancestral heredity, are too bad mix- 
tures to produce a uniform type, and under Mendel's law are too 
unstable to produce a constant type of any kind. The system 



628 PRACTICAL PROBLEMS 

of crossing is, therefore, best adapted to plants, which can be 
propagated asexually, and therefore free from the Hmitations 
just mentioned. 

Special Exercises 

Make calculations showing the relative expense of grading as compared 
with breeding pure for different classes of animals. 

Also make critical study of many pedigrees of famous animals in order 
to trace the systems of breeding actually employed, especially as to line 
breeding and inbreeding. 

ADDITIONAL REFERENCES 

Loss OF Vigor from Inbreeding. By H. J. Webber. Science, 1901, 

No. 320, p. 257. 
Pollination of Apples and Peas. Experiment Station Record, 

XIII, 620. 
Reciprocal Crosses (with extended bibliography). Maine Station 

Report, 1904, pp. 81-89. 



CHAPTER XVIII 

THE DETERMINATION OF SEX 
SECTION I — THEORIES 

The desire to control the sex, or at least to predict what it 
will be, is a very old and a very common one. There are 
apparently about as many theories purporting to cover the case 
as human ingenuity has been able to devise (more than five 
hundred are now known), ^ and as there is but one alternative in 
the case, any theory, no matter how absurd, is certain, under the 
law of probabilities, to come true half the time. Some of the 
principal theories that have gained popular credence, and which, 
so far as present knowledge goes, contain no basis of truth, are 
the following : 

1. That one testicle is naturally male, the other female, and 
that the sex will depend upon the source of the particular sper- 
matozoon taking part in fertilization. — Disproved by the fact 
that males with but one testicle are yet able to sire both sexes. 

2. That successive ova are alternately male and female, so 
that naturally the sexes would be evenly distributed, and all 
that is needed to produce sex at will is to choose the proper 
heat for service ; that is to say, if the last young were a female, 
then service at the first, third, fifth, etc., heats thereafter would 
produce males, and at the second, fourth, sixth, etc., heats would 
result in females. — Disproved in the same way as is the first 
theory ; that is to say, females with but one ovary produce 
both sexes, and the same sex is repeated indefinitely, with no 
alternation in heats. 

3. That the stronger personality, especially in a sexual sense, 
will impress its sex upon the offspring. — Disproved by the fact 
that parents of both sorts produce both sexes freely, and by the 
further fact that in general sires are better bred and stronger 

^ Geddes and Thomson, Evolution of Sex, p. 35. 
629 



630 frac:tic:ai, problems 

specimens than are clams, which should give a heavy pre[)()n- 
dcrance ol males, — a fact not substantiated. 

4. That service early in heat will produce a male (some say a 
female), and that service late in heat (with ovum stale) will 
produce the opposite sex. — Disproved by the fact that in 
nature females, especially in herds, are served early in heat, — 
a fact that should make the offspring practically all of one sex. 

5. That the older parent will determine the sex, — some say 
the jmrent nearest the jirime of life ; not substantiated. 

6. That extreme sexual excitement on the part of the female 
is almost certain to result in male (some say female) offspring. 
This is a difficult assumption to prove or to disprove, because 
everything turns upon what would be called extreme excitement, 
and the singular fact is that the believers in this theory them- 
selves appear cjuite unable to decide which sex is indicated by 
the violent disturbances of the female ; some say one, some say 
the other, until it looks like a case of the indigo test over again. 

It is inconceivable that the general disturbance of the body 
attending heat should have the slightest influence upon the 
character of the union of the nuclear matter of two germ cells, 
which is all that we now know to be involved in fertilization. 

It is noticeable that nearly every theory on determination of 
sex contains some trace of " male superiority," many going so 
far as to state that females are undeveloped males. This con- 
ceit is evidenced wherever an advantage is supposed to exist, as 
by excess of fertilization, — such advantage being always given 
to the male. 

Any theory not involving obscure distinctions — as does this 
one — can be easily proved or disproved by the statistical 
method, always remembering that a correlation up to 50 per 
cent is inevitable, indicating no cause at work but chance. It 
is far more profitable to leave speculation and inquire what is 
actually known about the causes that determine sex. 

Sex differences slight. First of all, the idea of fundamental 
sex differences is greatly exaggerated. About the only attribute 
that can be ascribed to " maleness " in general throughout the 
whole range of life is a little higher state of activity, usually but 
not always accompanied by somewhat decreased size. Typically 



THE DK TERM I NATION OF SEX 631 

the ovum is large, well supplied with nourishment, and not 
given to activity ; while the sperm plasm, spermatozoon, or 
pollen grain, is small, and poor in food material, but character- 
ized by great activity. 

Aside from this, males and females diffei' far less than is 
popularly supposed. The artificial conventionalities and the es- 
tablished divisions of labor exaggerate differences of sex in man, 
and over-enthusiastic writers have formed out of these exaggera- 
tions conclusions as far-reaching as they are grotesque. 

Sex differences are few and slight, and mostly connected with 
the serious business of reproduction. We need not, therefore, 
in seeking causes for their determination, look for such as strike 
at the very foundation of racial cliaracters. Sex is something 
superimposed upon all other considerations — not a fundamental 
division halving the population into (me section that may, and 
another that may not, enter into the full possession of all the 
endowments of the race. 

SECTION II — INFLUENCE OF NU'I'KITION 

In tadpoles. According to Pfliiger,' three forms develop: 
(a) distinct males, (d) distinct females, and (r) hermaphrodites. 
In the last case the male organs " develop round primitive 
ovaries, and if the tadpoles are to become males the inclosed 
female organs are absorbed." 

According to Young,^ sex in tadpoles remains a long time 
indeterminate, and during this time the amount of food exerts 
a controlling influence upon the sex. He had three broods of 
tadpoles. 

Brood I, under natural conditions, developed 54 per cent 
females, but when fed freely with beef it developed females in 
the proportion of 78 per cent ; the proportion of females from 
brood 2 was increased by a generous diet of fish, from 61 per 
cent to 81 per cent ; and in the same way a diet of frogs' flesh 
raised the proportion in brood 3 from 56 per cent when "left 
alone " to 92 per cent when fed, — all of which looks as though 
nutrition has some influence upon sex in frogs at least. 

^ Geddes and Thomson, The Kvolution of Hex, p. 45. - Iljid. 



632 PRACTICAL PROBLEMS 

In plant lice.^ In general it may be said that in summer, 
when favorable conditions of life are at the maximum, these 
creatures produce parthenogenetically generation after genera- 
tion, and only females, but with the cool of autumn and its 
lessened food supply, males appear, and sexual reproduction is 
resumed ; indeed, to quote from Geddes and Thomson, ^ " in 
the artificial environment of a greenhouse, equivalent to a per- 
petual summer of warmth and abundant food, the partheno- 
genetic succession of females has been experimentally observed 
for four years. It seems in fact to continue until lowering of 
the temperature and diminution of food reintroduce males and 
sexual reproduction." Others have stated that males may be 
produced at any time merely by letting the plants on which the 
lice are feeding become somewhat "dried up." 

SECTION III — INFLUENCE OF FERTILIZATION 

In bees.^ As is now well known, bees are of three forms as 
regards sex, — drones (males), produced from unfertilized eggs ; 
workers (females, generally but not always sterile), produced 
from fertilized eggs ; and queens (fertile females), also pro- 
duced from fertilized eggs but quartered in special cells and 
given large amounts of special food. As remarked by Geddes 
and Thomson, " royal diet and plenty of it develops the repro- 
ductive organs of the future queens," and at any time "within 
the first eight days of larval life the addition of a little food will 
determine the striking structural and functional difference 
between worker and queen." * This fact is often taken advan- 
tage of by the nurse bees when disaster threatens through the 
loss of the queen cells. Hastily extracting some worker larvae 
from their ordinary cells, they deposit them in the queen cells, 
giving them royal food, and speedily they acquire all the charac- 
ters of any other fertile queen, — a result plainly due either to 
the character or to the quantity of the food, or to both. 

In the case of bees, therefore, fertilization seems to be the 
deciding factor as to differences between male and female, and 

1 Geddes and Thomson, The Evolution of Sex, p. 49. 

- Ibid. p. 50. ^ Ibid. pp. 46-48. * Ibid. p. 47. 



THE DETERMINATION OF SEX 



633 



food the element that determines whether or not the female is 
to be fertile. This is a sex distinction that cannot hold in the 
higher forms, where fertilization is necessary to development, 
whatever the sex, showing that one species may differ from 
another, even in seeming fundamentals, and teaching us caution 
in making sweeping generalizations. 

In wasps. Von Siebold ^ conducted investigations with the 
fertilized and with the unfertilized ova of the wasp, Nematiis 
ventricosus, each kind of which produces both sexes tinder 
certain conditions. 

Development of Fertilized Ova 



End of Larval 
Period 


Number of Females 
TO 100 Males 


End of Larval 
Period 


Number OF Females 
to ioo Males 


Fifteenth of June . 

July 

July 


14 

77 

269 


August .... 
End of August . 
September . . . 


340 
500 
IOO 



From this we conclude that in general fertilized ova produce 

females, but not exclusively, the proportion of females being in 

some accord with temperature or food, or both. 

Here the unferti- 
,. 1 11 Development of Unfertilized Ov.a 

lized ova produced 

males except when 
the conditions of de- 
velopment were so 
favorable as to 
shorten the larval 
period to the utmost, 
leading Geddes and 
Thomson to remark 
that even "where 
the production of 

males is the normal condition, favorable environmental influ- 
ences appear to introduce females." 



Number 


OF 


Duration of 


Sex 


Experiment 


Larval State 


II 




21 days 


All males 


12 




19 days 


All males 


13 




18 days 


493 males, 2 females 


14 




17 days 


265 males, 2 females 


IS 




17 days 


374 males, 8 females 


16 




18 days 


168 males, i female 


17 




24 days 


1 male 



1 Geddes and Thomson, The Evolution of Sex, pp. 48, 49. 



634 PRACTICAL PROBLEMS 

SECTION IV — SEX IN MAMMALS 

Temperature and nutrition seem to be controlling factors in 
many of the lower forms, and when such is the case it is remark- 
able that in every instance the production of females seems to 
accompany the more favorable conditions, and that of males 
the harder or less favorable. 

Among mammals there is little experimental evidence, but 
that little points to the same general fact as found among lower 
animals, though the larger animals are manifestly less directly 
influenced by surrounding conditions. Girou divided a flock of 
three hundred ewes into two equal lots, one of which was ex- 
tremely well fed. This lot was served by two j/^//;/^ rams ; the 
other, scantily fed, by two mature ones. The well-fed lot (served 
by young rams) produced 6o per cent females, the other lot only 
40 per cent females.^ The difference in age of the rams intro- 
duces a second element, but the facts, if true, are significant. 

This is about all that is known of this phase of the question. 
Experimental evidence seems to indicate that abundant food, 
optimum temperatures, and generally favorable conditions tend 
to the production of females ; but when we come to predict the 
limits to which the rule will apply we must proceed with great 
caution, confessing that our exact knowledge is exceedingly 
limited. 

SECTION V — THE "ACCESSORY CHROMOSOME" AND 
SEX DETERMINATION 2 

Certain inequalities between germ cells in respect to the dis- 
tribution of chromatin matter have long been known.^ 

1 Geddes and Thomson, The Evolution of Sex, p. 51. 

2 Wilson (1906), "Studies on Chromosomes, \\\^^ Jonr}i(xl of Experimental 
Zoology, III, No. I, pp. 1-39. Also the following: Beard, The Determination of 
Sex; Castle (1903), "The Heredity of Sex," Bulletin of the Museinii of Com- 
parative Zoology, XL, 4 ; McClung (1902), "The Accessory Chromosome. Sex- 
Determinant.'" Biological Bulletin, \l\, i, 2; Morgan (1904), " Self-Fertilization 
Induced by Artificial y\.&2iX\%^'' Journal of Experimental Zoology, I, i ; Studies in 
Spermatogenesis with Special Reference to the Accessory Chromosome, Publica- 
tion No. 36, Carnegie Institute, Washington, D.C., September, 1905; Wilson, "The 
Chromosomes in Relation to the Determination of Sex in Insects," Science, XXII, 
564, October, 1905. ^ Wilson, The Cell, pp. 271-272. 



THE DETERMINATION OF SEX 635 

For example, Wilson reports that as long ago as 1891 Hen- 
king " discovered that in the second spermatocyte division of 
Pyrrhocoris one of the chromosomes passes undivided into one 
of the daughter cells (spermatids), which receives twelve chro- 
matin elements, while its sister receives but eleven"; so that, 
of the four resulting spermatozoa, two possess an additional 
chromosome as compared with the other two.^ 

Other discoveries were reported, and Paulmier (1898, 1899), 
working with Anasa in Wilson's laboratory, found that in the 
first spermatocyte division eleven tetrads appeared, one of which 
was " much smaller than the others " and seemed " to arise from 
a single nucleolus-like body . . . and by a process differing con- 
siderably from the others." He adds : " In the second (and last) 
spermatocyte division the (ten) larger dyads divide to form 
chromosomes in the usual manner ; tJie stnall dyad, however, 
fails to divide, passitig over bodily into one of the spermatids. 
In this case, therefore, half the spermatids receive ten single 
chromosomes, while the remainder receive in addition a small 
dyad." 2 

The fact was gradually established that, at least in Hemiptera 
and in certain other insects, one of the chromatin masses of the 
male maturation cell differs from its fellows, and undergoes one 
less division than they, so that, of the group of four spermatozoa 
arising out of the double division of the spermatocyte, two will 
possess an additional chromosome as compared with the other 
two. This additional member has been variously named by dif- 
ferent experimenters, the terms "accessory chromosome" and 
" heterotropic chromosome" being the most common. 

Here is about where the matter rested till McClung (1902) 
advanced the theory that the accessory chromosome is the sex- 
determinant, assuming (erroneously as we now believe) that if 
the ovum should be fertilized by one of the spermatozoa contain- 
ing the accessory chromosome the offspring would then be 
provided with the accessory and its sex would therefore be 
male ; while if the fertilization should be by one of the sperma- 
tozoa destitute of the accessory, the offspring would of necessity 
be of the opposite sex. 

1 Wilson, The Cell, p. 271. 2 ibid. p. 272. 



636 PRACTICAL PROBLEMS 

This view of the case made it appear that the female cells cor- 
respond most closely with those spermatozoa which are destitute 
of the accessory, and here the matter stood until Montgomery 
(1904), Gross (1904), and Wallace (1905) discovered that, in cer- 
tain species at least, the ovum has the same number of chromo- 
somes as the spermatozoa zvith the accessory. These experimenters 
came to the conclusion that " only one of the two classes of sper- 
matozoa is functional, namely, that in which the heterotropic (ac- 
cessory) chromosome is present. Those of the other class were 
assumed to degenerate, after the fashion of polar bodies." ^ 

Wilson (1906), shows that "the sexes in hemipters of this 
type do in fact show a constant difference in the number of 
chromosomes."^ He has determined, in at least four genera, 
that the number of chromosomes in the female cell corresponds 
with the larger number in the male cell; in other words, that the 
"accessory chromosome," though present in but half the sper- 
matozoa, is found in all female germ cells. This being true, the 
"remarkable" spermatozoa are not those witJi the accessory, 
but, on the contrary, those without it, and they are to be 
regarded as in some sense deficient. 

Wilson shows conclusively the opposite of Gross' and Wallace's 
hypothesis, namely, that when a female cell unites with a sper- 
matozoon destitute of the accessory chromosome, then the 
accessory of the ovum finds no mate and a male develops ; and 
that, on the other hand, if the ovum happens to be fertilized by 
one of the spermatozoa provided with an accessory, then each 
accessory finds its mate, there is then no solitary accessory, and 
a female results. 

Extending his experiments, Wilson finds two kinds of acces- 
sory chromosomes, — the one already described, which is smaller 
than the ordinary chromosomes, and another which is larger. In 
this connection it should be remarked that his investigations 
show great differences in size among the chromosomes generally, 
but that the "accessory" can readily be detected, whether 
larger or smaller than the others, and that all chromosomes, 
large or small, — except the accessory, — can readily be assigned 
in pairs under the microscope. 

^ Journal of Experinteittal Zoology, III, No. i, p. 3. - Ibid. 



THE DETERMINATION OF SEX 637 

It should be said in this connection, too, that in certain species 
the accessory seems always present, — in both spermatozoa as 
well as in all female cells, — but that when this is the case the 
accessories are distinguished by some kind of qualitative differ- 
ence not understood, but that gives to two of the spermatozoa 
of each group of four a different character from the other two. 

If, therefore, it shall appear that all female cells, after extru- 
sion of the polar bodies, are in possession of this accessory chro- 
mosome, whatever its peculiar quality, and if, out of each group 
of four spermatozoa arising from a single, spermatocyte, two are 
in possession and two are destitute of this accessory, then we 
have in the spermatozoa themselves a very evident fundamental 
cause of sex determination, and, as the numbers are equal, under 
the law of chance the sexes should be equal, as in fact they 
practically are. 

Here in truth would seem to be a fundamental cause of sex 
determination. Whether it is operative in all forms of life or only 
in certain species, it is yet too early to even speculate. A fertile 
field of inquiry is here opened up, and the near future may be 
expected to afford important additional data on this most 
difficult subject. 

Summary. There are various circumstances that appear to 
influence the sex of offspring. These seem, in some cases, to be 
connected with nutrition, and, in others, with the inherent nature 
of the germ. The present state of knowledge is insufficient to 
solve the problem of sex differentiation, but it is safe to say that 
none of the traditional beliefs are warranted by the known facts. 



ADDITIONAL REFERENCES 

Changing Sex in Plants. Tropical Agricuhure, 1903, pp. 789-790. 
Chromosomes in Relation to Sex Determination in Insects. 

By C. B. Wilson. Science, XXII, 500-502. 
Do Seedless Fruits Require Pollination ? Experiment Station 

Record, XV, 1080. 
Experi.mental Zoology. By T. H. Morgan. Chapters XXIV-XXVII. 
Experiments in Heredity and Sex Determination in Moths. 

Report of the British Association for the Advancement of Science, 

1904, p. 594. 



638 PRACTICAL PROBLEMS 

Influence of Nutrition on Sex. Experiment Station Record, XVI, 

228. 
Parthenogenetic Fertilization in the Honeybee^ Experiment 

Station Record, XV, 792. 
Recent Theories in Regard to Determination of Sex. By T. 

H. Morgan. Popular Science Monthly, LXIV, 97-116. 
Sex Control. By Professor Schenck of Austria. Science, VII, 736- 

738. 
Sex Determination in Bees. (A discussion of the Dzierzon-Dickel 

controversy.) By B. Sporrer. Experiment Station Record, XI, 561, 

657, 956. 
Sex Determination, — whether Bud shall be Leaf or Flower. 

By E. S. Goff. American Garden, igoi, pp. 330-333, 346-347. 
Sex in Mice. By Parsons and Copeman. Proceedings of the Royal 

Society, London, LXXIII, 32-48. 
Sex in Plants a Matter of Nutrition. By T. Mehan. Report, 

Department of Agriculture, 1898, pp. 536-548; Experiment Station 

Record, XI, 910. 
Wisconsin Experiment Station Report, 1900, pp. 266-285 ; 1901, 

pp. 304-316. 
Ziegler's Theory of Sex Determination. By T. H. Morgan. 

Science, XXII, 839-841. 



CHAPTER XIX 

PLANT BREEDING 

When the principles of breeding are once understood, their 
appHcation to special cases, either in plant or animal breeding, 
is largely a matter of common sense, and no extended discussion 
of particular operations is necessary. 

It has already been remarked that the breeder needs the 
utmost possible familiarity with the particular line he hopes to 
improve. This familiarity he will get largely through experience, 
but he cannot afford to neglect any source of information that 
will enlarge his acquaintance with the breed or the variety, for 
every item of knowledge will constitute a valuable asset in his 
business when the time comes, as it surely will, for weighing 
slight differences in the balance in order to determine questions 
of selection. This involves detail which only the practical 
breeder can acquire, and upon which attempted instruction 
amounts to little more than academic dissertation. Certain 
special facts and principles, however, run through plant breed- 
ing, as distinct from animal breeding, and these it is well to 
clearly understand in advance of actual operations. 

SECTION I — ADVANTAGES AND LIMITATIONS 

Advantages in plant breeding. The plant breeder possesses no 
less than six distinct advantages as compared with the breeder 
of animals : 

1. Large numbers, giving excellent opportunity for selection. 

2. Rapid reproducing powers, resulting in a marvelous saving 
of time as compared with that necessarily consumed in the 
slower process of animal breeding. 

3. The relative cheapness of individuals, making wholesale 
destruction economically possible. 

639 



640 PRACTICA], TROBLKMS 

4. The greater likelihood of mutations arising from mere 
point of numbers, if from no other cause, and the greater ease 
with which these may be detected if they do arise. 

5. The greater chance of preserving mutations, owing to 
rapid powers of reproduction. 

6. The possibility of reproducing asexually by budding, cut- 
ting, etc., which overcomes to a large extent the disasters of 
sterility and avoids the operation of Mendel's law in the propa- 
gation of hybrids. 

The plant breeder, therefore, not only enjoys superior advan- 
tages in selection, but he is free to make full use of mutations 
and the principle of crossing, — two forms of improvement all but 
closed to the animal breeder. Naturally, therefore, his operations 
assume one of three well-defined forms or systems of breeding : 

1. "Straight selection," or breeding from the best, the pur- 
pose being the improvement of existing varieties rather than the 
production of new strains. 

2. Maintaining extensive plantings in the hope of detecting 
spontaneous mutants, the object being the production of new 
varieties. 

3. Crossing, or hybridizing, with the purpose of producing 
new strains. 

New strains produced by either the second or the third method 
are of course variable and capable of improvement by straight 
selection. Each system of breeding requires its own methods, 
suited to the material in hand and the character of the improve- 
ment sought. Some species do best with one system, others 
with another, and only experience can decide which is most 
prolific of results in a particular case. The first, straight selec- 
tion, is the safest, and is ahvays certain of results ; but most 
species respond well to the second and the third, which, with 
suitable material, are capable of the richest results known to all 
breeding, and are the systems par excellence for the production 
of new strains. 

Crossing has latterly fallen into some disrepute because of 
the emphasis laid on Mendel's law, and the principle of mutation 
is but recently recognized ; but the prediction is ventured that 
the former will be restored to favor in plant breeding, and that 



PLANT BREEDING 64 1 

mutation will yield unexampled results in certain species that are 
"in the mutable state." 

Limitations and disadvantages of the plant breeder. It is not 
all clear sailing for the plant breeder. He has no less than six 
distinct limitations which he must recognize in advance : 

1. His varieties are subject to the effects of soil and climate 
in a way quite unknown to the animal breeder. His operations 
are, therefore, in a large measure local rather than general in 
their results. 

2. The rapid rate of reproduction necessitates wholesale 
destruction, with the almost certain loss of "good things." 

3. It is impossible to prevent accidental crossing of many 
varieties by insects and by the wind. 

4. It is difficult to keep accurate records. 

5. The product is cheap and it can be readily and rapidly 
reproduced by every novice the moment it is on the market. 
This necessitates that the breeder shall operate as a seedsman 
in order to secure financial returns for his labors, or else that 
he shall sell his production to those who are seedsmen. 

6. The extravagant claims often made for new varieties 
possessing little or no merit tend to destroy confidence in new 
creations. This attitude on the part of a portion of the trade 
leads the public to discount heavily even the moderate state- 
ments of reputable seedsmen, reducing by a considerable per- 
centage the profits of the business. 

Two of these natural limitations, — the limitations of the soil 
and the difficulty of keeping accurate records, — call for special 
attention. 

SECTION II — SOIL AND CULTURE CONDITIONS 

The breeder is all but powerless to alter climate conditions, 
but the fertility of the land is absolutely under his control. 
Should the soil for breeding operations be rich or poor ? at, 
below, or above the average of that upon which the crop is 
likely to be grown } 

The argument is often advanced that if breeding operations 
be carried on upon land below the average of fertility, then the 



642 PRACTICAL PROBLEMS 

strain will prosper even better in the hands of the farmer, and 
thereby stand more chances of pleasing when put to the actual 
test on the farm or in the orchard. Specious but faulty, is the 
only correct verdict as to this position, though it may be main- 
tained, perhaps, as to some special strains particularly sensi- 
tive to high fertility. Improvement is what is aimed at by the 
breeder, — the production of better strains than before. On 
this there are two significant points : 

1. The breeder will not know when he has succeeded in pro- 
ducing an improvement unless the soil conditions are good 
enough to permit full and complete development. 

2. All experience goes to show that plants are more variable 
in soils of high fertility than in soils of low fertility. This is the 
experience of De Vries, of Darwin, and, so far as is known to the 
writer, of every plant breeder upon record. 

The object in all plant breeding is the production of improve- 
ment. This is partly dependent upon fertility, and, in general, 
plant-breeding operations will be most successful on lands of 
maximum fertility. Some acclimatization may afterward be 
necessary as to soil as well as to climate, but the latter is 
involved in all plant breeding, — and the former too, for that 
matter, — for no soil can be fairly representative of any very 
great extent of territory. 

The balance of fertility. Much remains to be learned as to 
the elements that should predominate in a fertile soil. In 
general, nitrogen favors the growth of leaf and stem, but there 
is much reason to believe that seed formation is intimately 
related to the supply of phosphorus. The botanist will tell us 
that Saprolegnia, for example, grows luxuriantly in beef extract 
or peptone, but produces no reproductive organs ; grown in 
nutrient solutions containing abundance of phosphorus, how- 
ever, reproductive organs form readily, especially in the female. 

Without doubt much remains to be learned in the matter of 
making up of soils most favorable for the production of desirable 
variations in different classes of plants. In this matter of soil 
fertility and cultural requirements let the plant breeder provide 
maximum conditions, with no fear of evil consequences. If he 
can succeed in producing a desirable variety by hook or by 



PLANT BREEDING 643 

crook, acclimatization will come to his aid and help him to 
preserve it. 

Of one fact we may be well assured, namely, that every plant 
is at its best under optimum conditions. That is the time when 
favorable variations may be most confidently expected ; in other 
words, that is the time when it will respond most favorably to 
selection. The writer believes this to be the general principle 
from which to work out the conditions under which the particular 
strain or strains yield best results, but the plant breeder must 
not deceive himself into thinking that he will get valuable devi- 
ations from type while the plant is enduring hard conditions, the 
effect of which is to bring everything to the dead level of medi- 
ocrity, where little improvement is possible by breeding without 
first improving the conditions of growth. 

SECTION III — SYSTEMS OF PLANTING 

In general, three systems of planting are in use among plant 
breeders : 

1. The nursery system, in which the plants are treated as 
individuals, each being given abundance of room, and each made 
the basis of selection at the close of the season. 

2. The field system, in which individual plants are not given 
special opportunities. Seed is saved from the best plants, but 
no attempt is made to identify and isolate particular parentage. 
This is " improvement " rather than breeding, and is in common 
use among general farmers. 

3. What Webber calls the Burbank method of crowding 
thousands of seedlings close together on good soil and then 
selecting the few that are able to endure the battle and survive. 

Each system has its advantages, especially the first and third, 
but the third merges into the first the moment that really close 
work begins. 

All things considered, it is altogether likely that the greater 
part of our results will be obtained by the so-called nursery 
method. In any event this is the method that lends itself to 
the best grade of work and to the most complete records. It is 
the one therefore that will receive further consideration here. 



644 



PRACTICAL PROBLEMS 



Plot or row in the nursery system. Shall the individuals of a 
single selection be planted together in rectangles or grown in 
separate rows ? Each system has its advocates, and the matter 
is to be decided first of all by convenience in cultivation and 
harvesting, and second by convenience in keeping records. The 
two systems are well illustrated by the methods employed at 
the two experiment stations of Minnesota and Illinois. 

The plot system. This system is best described by its use at 
the Minnesota station, where it has been fully elaborated and is 
constantly employed for all breeding work.^ Under this system 
as there employed the procedure is substantially as follows, 
taking wheat as an illustration. When a new variety is received 
or a promising plant is selected its history is recorded on a 
record sheet 5|^ X 8^ inches and punched at the end for filing. 
It is given a class name and a number of its own (" Nursery 
Stock No. — "), and if it sprang from a numbered stock, that 
number is also recorded as " Parent Stock No. — ." This sheet 
is known as the " Introductory Sheet," and is reproduced here 
on a reduced scale. 



Form 61 



SELECTED STOCK— INTRODUCTORY SHEET 









Nursery 

Stock No 


\X/I-rPAT Class Name of 
wnE,/\i Parent Stock . 


Minn. No. of 

Parent Stock 








Date 


Origin and History of 


Parent 


Stock 





The seed is then planted by itself in a rectangular plot, ten 
plants square if possible, — hence known as a " centgener 
plot." Notes are taken both on the centgener plot as a whole 
and on individual plants, and recorded on sheets (see table on 
opposite page, reduced size). 



'^ ?>ee. Bulletin A^o. 62, Minnesota Agricultural E.xperiment Station, for a full 
description of the plot system as used at this station. 



PLANT BREEDING 



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Manifestly all the plants 
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The system seems some- 
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The row system. This 
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648 PRACTICAL PROBLEMS 

Under this system each ear of corn, for example, is planted 
in a separate row, and as many rows will be used as there are 
ears in the first selection. The ear in the book and the row in 
the field then have the same number. 

Suppose we are starting an experiment on breeding for " high 
oil." It is the first year, and we have the twenty highest oil 
ears that could be found out of the seed at hand. These ears 
will be numbered, not from i to 20, but from 10 1 to 120. 
Next year they will be numbered 201 to 220, or 225, or to what- 
ever number of ears may be available. The hundreds always 
show the number of years or generations of improvement, and 
the rest of the number shows the field number of the ear and of 
the row in which it is planted. Thus, if we find ear No. 612, 
we know that it is the sixth year of the experiment, or the 
sixth selection from the original stock, and that it is planted in 
row No. 12 of that year's field. This ear, like all others that 
have been analyzed, has its laboratory number, or " annual ear 
number," by which its composition may be traced ; but its 
"pedigree number," 612, for example, is the one from which 
its breeding is traced. A sample page from such a register 
book shows the system in full, there being no other records 
except the chemical analyses. This is the entire record of the 
high-oil corn for 1902. (See table on opposite page.) 

Selecting 607 of this table, for example, we see by the record 
that its dam of the year before was No. 504 ; that its number 
in the chemical laboratory was 3923 ; that the ear was 6.5 
inches long, its tip circumference 4.8 inches, and its butt cir- 
cumference 5.8 inches; that it had 12 rows, and that each row 
had an average of 48 kernels ; that the ear weighed 5.3 ounces, 
and had 7.13 per cent of oil. We learn, too, that it was planted 
in row No. 7, which was 7i^\ hills long and produced 85. pounds 
of corn, or at the rate of 63.5 bushels per acre; that there 
were in all 140 ears of corn in the row, the average oil content 
of which was 6.65.^ 

As a practical detail in corn breeding, it may be remarked 
that the best ears are always planted in the middle rows to give 
them the advantage in the matter of pollination. 

1 As determined by a composite sample of twenty average ears. 



PLANT BREEDING 



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650 PRACTICAL PROBLEMS 

As between the two systems the individual must take his 
choice. The row system seems to have the advantage of sim- 
pUcity, especially for plants standing in cultivated rows. It is 
the one most readily understood and most easily managed by 
the farmer, but either is easy of application. 

The performance record. One of the surprises of plant breed- 
ing is the very different appearance of the progeny from equally 
promising individual ears, heads, or other selection. A differ- 
ence of two to one is not at all uncommon, and not infrequently 
a row or centgener plot from promising seed proves almost 
worthless. Hence the necessity of accurate records of entire 
rows and centgener plots. ^ There is little use in wasting time 
on inferior material, for the best individual plant from such a 
fraternity would be but poor stock for breeding purposes. All 
individual selections for future planting, then, should be made 
from rows (or centgener plots) with a high average perform- 
ance record. 

Multiplying plots and fields. After a new strain has proved 
satisfactory in the nursery row or plot, it must needs be "mul- 
tiplied " in order to secure a sufificient quantity for sale. It is 
usually customary to select for at least three generations, as in 
the production of sugar-beet seed, then multiply by planting 
out in the open field and seUing the total crop for seed. Thus 
the beet seed of the market is generally two "removes" from 
the " mother beet," whose selection was made by sugar content. 

Seed production a business. It is fashionable to advise the 
farmer to produce his own seed. From the standpoint of 
acclimatization it is good advice, but from any other standpoint 
it is bad counsel, providing, of course, that plant breeders and 
seedsmen live up to their responsibilities. 

It is unthinkable that the farmer who is primarily engaged in 
production can also be a skilled improver in all that he produces. 
He may breed one or two lines of animals or plants himself, 
and if he be a breeder by nature and training, and if he have 
the leisure, that is well ; but by the same token he should 

1 The row of the row system corresponds, of course, to the centgener plot 
of the plot system, and lioth include the entire progeny of an "individual 
selection." 



PLANT BREEDING 65 I 

expect some other specialist to provide him with his foundation 
stock in other Unes. No man living, or that will ever be born, 
will succeed in breeding all lines of animals and plants, except 
to their confusion and general degradation. 

So while it is popular to advise the farmer to produce his 
own -seeds, it is better business policy for him to buy, and spend 
a little time and patience in acclimating the strains if need be 
for a year or two, before putting the new stock into common use. 
This will generally suffice, and if, in a special case, as perhaps 
in corn, no improved variety will successfully acclimate, then 
there is nothing to be done but to set about the production of 
an improved strain of the local variety ; but this can be accom- 
plished by a few persons or even by one person as well as it 
would be done if every neighbor undertook the task. 

Improvement, even in plants, is costly business, and when 
once it is effected a real investment has been made that can be 
multiplied as often as men and lands are available. 

The interests of agriculture demand that some men give their 
time and genius to the improvement of animals and plants. 
Their number, however, will never be relatively large, and it 
need not be. It is expedient that all farmers address themselves 
to the serious business of learning how to handle and produce 
on a commercial scale the really excellent creations in plant and 
animal life that the genius of breeders is able to originate. 



ADDITIONAL REFERENCES 

Abstract of Papers read at the New York Conference of Plant 
AND Animal Breeders (September 30-October 2, 1902). Experi- 
ment Station Record, XIV, 208-222. 

Bibliography. (A reference to forty-eight articles on plant breeding.) 
Experiment Station Record, XV, 770; also in Experiment Station 
Record, XVI, 354, thirty-one articles. 

Breeding Animals and Plants. By VV. M. Hays. Breeders' Gazette, 
XLI, 892,944. 

Breeding Corn. By C. P. Hartley. Year Book, United States Depart- 
ment of Agriculture, 1902, p. 539. 

Breeding Cotton. By H. J. Webber. Year Book, United States Depart- 
ment of Agriculture, 1902, p. 365. 

Breeding for Earliness. Experiment Station Record, X, 352. 



652 PRACTICAL PROBLEMS 

Breeding Peanuts. North Carolina Experiment Station, Bulletin No. 
168, pp. 421-434 ; also in Experiment Station Record, XI, 1032. 

Breeding Wheat. By William Saunders. Agricultural Science, 1899, 
74-87; also in Experiment Station Record, XII, 339. 

Breeding Work of the Minnesota Experiment Station. By 
W. M. Hays. Breeders' Gazette, XLIV, 11 87. 

Coffee Hybrid. Gardener's Chronicle, 1899, p. 240. 

Cooperative Breeding. By W. M. Hays. Breeders' Gazette, XLV, 14. 

Cross, Maize-Teosinte. By J. W. Harshberger. Garden and Forest, 
1896, p. 522 ; also in Experiment Station Record, VIII, 563. 

Cross-Breeding of Fruits. (Summary of series of experiments cover- 
ing a number of years.) By J. L. Budd. Iowa Horticultural Society, 
1900, pp. 176-178; also in Experiment Station Record, XIII, 454. 

Crossing of Peas, Beans, etc. Experiment Station Record, XVI, 263. 

Crossing Strawberries. By F. W. Card and G. E. Adams. Rhode 
Island Experiment Station Report, 1900, pp. 247-267; also in Experi- 
ment Station Record, XII, 944. 

Crossing Varieties. By B. D. Halsted. New Jersey Experiment Sta- 
tion Report, 1901, pp. 389-41 I ; also in Experiment Station Record, 
XIV, 568. 

Difference in Plant and Animal Breeding. By W. M. Hays. 
Breeders' Gazette, XLIV, 1132. 

Effect of Soil on Development. Experiment Station Record, XVI, 22. 

Experiments in Plant Breeding on the Dominion Experimental 
Farms. By William Saunders. Transactions of the Royal Society 
of Canada, 1902, p. 115. 

Experiments of Luther Burbank. By David Starr Jordan. Popular 
Science Monthly, LX\'I, 201-225. 

German Method of Breeding Sugar Beets. Experiment Station 
Record, XIII, 642-948. 

Hybrid, Blackberry-Raspberry. Experiment Station Record, VII, 
36, 306. 

Hybrid Corn. By C. P. Hartley. Year Book, United States Department 
of Agriculture, 1902, pp. 539-550. 

Hybrid Tomatoes. Experiment Station Record, XI 1 1, 348. 

Hybridization. (Lists of hybrids and general laws of heredity.) By 
F. A. Waugh, American Garden, 1899, No. 234, p. 431. 

Hybridization. Papers by Bateson, DeVries, Bailey, and Webber. 
Science, X, 1 13-1 16. 

Hybridization in Beans. By R. A. Emerson. Nebraska Experiment 
Station Report, 1903, pp. 33-68 ; also in Experiment Station Record, 

XVI, 563-564- 

Hybridization of Barley, Wheat, Oats, and Fruits. By William 
Saunders. Transactions of the Royal Society of Canada, 1894, 
pp. 139-142 ; also in Experiment Station Record, VII, 273-275. 



PLANT BREEDING 653 

Hybridization of Cereals. By J. H. Wilson. Report of the British 

Association for the Advancement of Science, 1904, p. 796. 
Hybridization of Rve. By P. Nielson. Experiment Station Record, 

VII, 204. 
Hybridizing Roses and Gooseberries. By J. L. Budd. Iowa Experi- 
ment Station Bulletin No. 36, p. 868 ; al.so in Experiment Station 

Report, X, 47. 
Methods of Planting and Systems of Keeping Records. By 

W. M. Hays. Breeders' Gazette, XLII, 10, 42, 124, 255. 
Philosophy and Practice of Breeding. By Luther Burbank. 

Popular Science Monthly, 1905, pp. 201-225. 
Profitable Breeding by Improving Existing Varieties. By L. H. 

Bailey. Year Book, United States Department of Agriculture, 1896, 

pp. 297-304. 
Reversion and Graft Hybridization. By H. J. Webber. Science, 

1896, No. 92, pp. 498-500. 
Strawberry Breeding. By N. O. Booth: American Garden, 1900, 

p. 534 ; also in Experiment Station Record, XII, 246. 
Use of Immature Seed gives Inferior Trees. By T. Christy. 

Gardener's Chronicle, 1896, p. 145; also in Experiment Station Record, 

VII, 588. 



CHAPTER XX 

ANIMAL BREEDING 
SECTION I — ADVANTAGES AND DISADVANTAGES 

Advantages. Animal breeding possesses three substantial 
advantages over plant breeding : 

1. More freedom from climatic and other local conditions, so 
that the product is fitted for a wider range of service. 

2. Relatively good prices, because the individual has a high 
value and is not so easily or so rapidly multiplied. 

3. Involving superior beings, animal breeding becomes one of 
the highest forms of art. In this we are dealing not only with 
superb physical form, but with mental qualities as well, and here 
the breeder may come into sympathetic personal relations with the 
products of his hand and of his genius. The same sympathetic 
relation will be claimed by the lover of plants, and especially by 
the lover of flowers ; but the fact remains that only with animals 
do we find consciousness and intelligent response to our moods 
and passions. What feeling on earth, outside of human affection, 
can approach the attachment existing between a man and his 
horse, or between a dog and his master } 

Disadvantages. But the animal breeder must face a long line 
of limitations and disadvantages. Some of these can be easily 
singled out and stated, others are too subtle for putting into 
words : 

1. Numbers are necessarily few, and reproduction is relatively 
slow, making selection difficult from mere scarcity of material. 

2. Individuals are costly, and those of high breeding powers 
extremely so. This makes really good breeding not only ex- 
pensive but in a measure hazardous, for prices have a way 
of taking a sudden drop, often with little or no warning 
when nothing better than the open market affords an outlet 
for surplus stock. 

654 



ANIMAL BREEDING 655 

3. The characters to be selected and bred for are generally 
not few but many, and difficulties in selection necessarily increase 
out of all proportion to the number of points to be attained. 

4. As if the breeder did not have troubles enough of his own, 
fashion is continually adding points that demand his attention 
most imperiously, even at the expense of better things. 

5. Animals propagate but slowly, and breeding operations 
necessarily extend over many years and several generations ; the 
population cannot, therefore, be spread out to view, and there is 
more or less uncertainty as to actual family history and individ- 
ual merit, — all of which makes selection more or less difficult 
and uncertain. 

6. The young of most animals are promising, but selection 
cannot safely be made at extreme immaturity, for the differ- 
ences between inferiority and superiority are brought out only in 
the development that comes with full maturity. TJie excellence of 
breeding is niaitily shozvn in the capacity for development, and 
this cannot be foretold except as it may be predicted by a 
general knowledge of the particular family line and the spe- 
cial blood combination involved. Some of the most promising 
"young things" are the bitterest disappointment. 

7. Animals are difficult of development, and many of the 
best-bred things are never properly developed. 

8. Animals do not reproduce asexually, and their successful 
production is conditioned upon high sexual fertility. Now, imper- 
fect sexual development is one of the most common, if not the 
most cojmnon, defect in both plants and animals. Plants may be 
propagated by buds or cuttings, but animals are at the mercy of 
sexual reproduction. In nature the existing lines are kept at 
least fairly fertile by natural selection, but in domestication no 
such controlling influence exists unless supplied by the breeder 
himself. This lack he must provide for if he hopes to succeed, 
but it constitutes one of his principal difficulties. 

9. Fashion and custom decree that animals shown at the fairs 
shall be put into extreme condition, and this is a constant menace 
to the efficiency of a breeding herd. 

10. A strong vein of speculation has entered into many lines 
of animal breeding, the tendency of which is to unsettle prices 



656 PRACTICAL PROBLEMS 

and conditions generally in what ought to be one of the most 
steadily conducted of all the industries. 

These, in brief, are some of the limitations of the animal 
breeder. He cannot afford to close his eyes to their existence, 
for they are realities. He will get on best to frankly confess their 
existence and to meet them to the best of his ability. It remains 
to examine a little more closely into some of these and other 
detailed considerations that must engage the breeder's attention. 

SECTION II— FEWER CHARACTERS FOR SELECTION 

The greatest single improvement possible in present-day 
animal breeding in most lines would be to free the situation 
from unimportant characters. At best the breeder must pay 
regard to a large number of considerations in making selections. 
Constitutional vigor, high productive powers, and utility for the 
purpose in mind are fundamental considerations, and the last 
(utility) is more than likely to cover many points. 

Now the difficulties of selection increase at a surprising rate 
as requirements multiply. If a proper degree of constitutional 
vigor is found in but one animal out of two, — and it is not 
higher than that, — then the chances of a particular animal prov- 
ing satisfactory in this respect are but one out of two, or, as we 
say, his probability is ^. If, again, but one animal out of three 
'vs, fully fertile,^ — and it is doubtful if the proportion is higher, 
in certain lines at least, — then the chances of a strong constitu- 
tion and full fertility being found in the same animal are but 
^ X ^, or ^. If, now, we add to this a third requirement found, 
say, in but one animal out of ten, then our chances have been 
reduced to i- X ^ X j'q = g^^, which is equivalent to saying that 
only one animal in 60 taken at random — that is, but one animal 
in 60 of all that are born into the breed — will fully meet our 
demands and satisfy our requirements, except in so far as the 
characters in question viay be related by causation and to that 
extent overlap. 

^ By full fertility is not meant the power to reproduce as against absolute 
barrenness, but rather full and maximum powers of reproduction, — that is, regular 
breeding throughout a reasonably long life. 



ANIMAL BREEDING 657 

If, now, to this we add, say, three other requirements ("points ") 
represented respectively by ^, ^V, and ^V, we have reduced our 
chances to i^ X ^ X ^\ X ^ X ^V X o^. oi" 1 15^200, — meaning 
that not one individual in 100,000 will meet our demands. But 
this is beyond the range of practical selection, and it means that 
defects will of necessity be accepted. If the same defect were 
always accepted the damage would be less, but in practice one 
point is now waived and then another, as we choose the least 
of two evils, and so defects linger and, behaving according to 
the principles of Mendel's law, return to plague us long after 
we supposed ourselves through with them and well freed from 
their influence. This is really mixed breeding, however pure 
the pedigree. 

Now the principle is this : we should tolerate no more points 
at any one time than can a// be found in the same individuals. 
When the entire population come to possess these few charac- 
ters in a high degree, then other requirements can be safely 
added, because t/ie breeding for a fe^cv cJiaracters at a time 
amounts to practical certainty. The breeds with which this 
method has been practiced — racing horses and hunting dogs, 
for example — have outstripped anything known in the rapidity 
of their improvement, and, moreover, a foundation has been se- 
cured on which other requirements may safely be laid ; whereas 
the breeds in which many requirements have been exacted con- 
temporaneously have had a checkered history, full of ups and 
downs, and the end is not yet, — nor will the end be in sight 
until the custom is abandoned of requiring at the same time so 
many points as to put the matter beyond the range of practical 
selection. 

The direct effect of too many points of selection is, first, 
temptation to overlook, under the stress of circumstances, those 
fundamental biological requirements, — constitution and high 
breeding powers ; and history shows that this has been repeat- 
edly done, to the extinction of some of our otherwise most 
promising creations. When this result does not follow, the 
inevitable consequence of too many points of selection is that 
we are forced to accept defects, now one and then another, as 
has been shown, until, under Mendel's law, the breed becomes 



658 PRACTICAL PROBLEMS 

at best a mixture; of good and evil, — a mixture, moreover, that 
will never purify itself, and that can be purified only by a return 
to first principles. 



SECTION III — FASHION 

As fashion decrees the cut of our clothes, so it also decrees 
the length of the tail of a cow or the shape of her horn, and the 
height at which a horse should raise his feet from the ground. 
If fashion would be reasonable, and consistent, and stable, it 
would not be so bad, for breeders could finally adjust themselves 
to its demands ; but it is not stable, and often it is neither 
reasonable nor consistent. 

Now it is not so easy to change the conformation of an animal 
as it is to alter the cut of a garment, which means at the most 
only a turn of the shears this way or that. Every one of these 
decrees of fashion indicates an additional requirement for selec- 
tion, and we know what that means to the breeder ; not only 
that, but such decrees are certain to be short-lived, changing for 
others more or less troublesome. Worst of all, many of these 
requirements of fashion are to the distinct and j^crmanent dis- 
advantage of the breed — that is, permanent until bred out, 
which we have learned requires approximately six generations 
of successful selection. 

But the mandates of fashion are to be reckoned with, erratic 
and troublesome though they may be, for in a very large measure 
they detcnnine sales and Jix pi ices. Now the breeder is in the 
business for money, and he must sell stock or abandon all hope 
of profit, — which in the end means to abandon the enterprise 
entirely ; and no phase of practical breeding calls for more wis- 
dom and shrewdness than this particular problem, — how to 
meet the changing demands of the market and keep the herd or 
stud intact and if possible improving. 

In so far as these fashions emanate from the open market 
their control is practically beyond the breeder. But some of the 
worst of them emanate from among the breeders themselves, who 
sometimes seem bent on inventing artificial issues on which to 
make sales. Sometimes there comes a feeling, apparently, that 



ANIMAL BREEDING 659 

there arc too many animals of a given breed available, and thai, 
in self-protection, new standards must be set u[). 

This is confusing to the buyer and only hurtful to the breed- 
As a matter of fact, there never were and never can be too many 
really excellent animals of any breed. The question of develop- 
ing the market for pure-bred stuff will be discussed later, but here 
it is enough to say that no artificial standards should be tolerated 
in any breed merely to create sales. This matter can be con- 
trolled by the breeders themselves in their own associations, and 
when it is controlled a large share of the senseless and disturbing 
"decrees of fashion" will have disappeared and the remaining 
ones will have been mostly modified into comparative harmless- 
ness. There is too much homemade law passing from mouth to 
mouth among breeders, without the sanction of associations, and 
much of it would never be seriously supported on any floor if the 
advocates were really required to seriously defend it. Here is a 
duty that every association owes the breed it advocates and 
whose interests it maintains. 

But when all is said and done, how shall the individual proceed to 
meet the decrees of a craze that in his judgment will s[)eedily pass .? 

There is no better way than by the use of sires that strongly 
possess the points demanded in the market, always being care- 
ful to preserve a goodly number of the best females uncontami- 
iiated from the infection. These will form the nucleus of the 
new herd or stud after the craze has passed and the pendulum 
has swung back to the normal. 

Here the breeder must be wise in his judgment as to whether 
a new thing is only a passing craze or is really a permanent 
improvement in the breed, and here his accumulated knowledge 
of animals will serve him well ; but he should be well advised 
that by the proper use of the sire a herd may be made to turn 
out a new style of animal for a considerable time without in any 
way affecting the real char'acter of the foundation, and this can be 
continued as long as the old ^X.ock of females lasts. As the time 
of their end approaches, however, something must be done to 
restore their number, or else the new point must be accepted and 
bred into the females which really constitute the backbone of 
every producing herd. 



66o PRACTICAL PROBLEMS 

SECTION IV — SHOW-RING CONSEQUENCES 

Animals that have made their record in the show ring are 
none the worse for that fact, and this success adds greatly to 
their credit as individuals and to the commercial value of their 
get afterward. Although the excessive fitting required in the 
ring is often injurious, it is not necessarily so. It is of course 
true that no animal will remain long in "form," nor can the 
process of fitting be repeated many times. Show-ring animals 
are thus often a disappointment to the eye later on, but this is 
no detriment to their breeding powers. The only danger from 
excessive fitting is its effect upon fertility, and if this has been 
impaired it will very soon become evident. 

It is a serious question as to wJicn a breeder can afford to 
take the risk of putting into the ring a valuable breeding animal. 
As a matter of fact, if not of necessity, most show animals are 
young. The writer does not share the opinion that show-ring 
animals have necessarily been injured for breeding purposes, any 
more than he shares the opinion that show-ring success is a 
guaranty of breeding powers. Upon this point nothing is reli- 
able but the actual test. 



SECTION V — TESTING OF SIRES AND DAMS 

When we remember that variability cannot be reduced below 
89 or 90 per cent of the variability of the race, or, in extreme 
cases, perhaps to 85 per cent, and when we appreciate the fact 
that no matter how much the type (or mean) has been improved 
the variability remains, then we are no longer surprised at the large 
number of mediocre individuals that appear even in blood lines 
the most aristocratic and that have been longest " in the purple." 

The necessity for selection, therefore, will always exist, and 
when we add to this that other fact, that many mediocre-/f?^/^/;/^ 
animals are after all great breeders and many exceptional individ- 
uals bitter disappointments, there is an additional reason for 
the actual test. 

And still again, no one knows positively what will be the 
result of a new combination of blood lines until it has been 



ANIMAL BREEDING 66l 

tried ; thus, by every count, we arrive at the conclusion that 
real progress is assured only with tested animals. 

Testing dams. The test of a dam is what she has produced. 
If the herd has been bred by the owner, — and in general no 
other course is consistent,- — then the records of the herd will 
show the breeding powers of every female in it, and any one 
that is not satisfactory should be promptly eliminated. If this 
course is pursued, then at any given moment the owner of an 
established herd will be in possession of a tested herd, so far as 
the females are concerned, and the only additional testing is of 
each new sire that is brought into service.^ 

This is a comparatively simple matter if the breeding powers 
of the female side of the herd are well known. If they are not 
well known, the breeder is worse off than the ship at sea without 
rudder or compass ; he may multiply animals, but he will never 
do much real breeding. If a female is brought into the herd, she 
should on all accounts be brought in on her breeding record if 
possible ; for, of a hundred females, only a few will prove great 
mothers or even good mothers. If, of necessity, young females 
are put into the herd, then they must be regarded, like the regu- 
lar produce of the herd, as under a test until each shall prove 
herself a breeder entitled to a place in the permanent herd. 

Testing young females. This is a job that the breeder has 
always at hand. His herd is short-lived at the best, and however 
good it may be it will become extinct by death in a few years 
unless reenforced from younger stock. 

While individuals live many years, it is found in actual prac- 
tice that the cJiaractcr of the entire herd will change in five 
years with cattle and horses, and in much less time with sheep 
and swine, unless properly reenforced with young animals. A 
breeding herd is a moving tide of life, and what the breeder 
does he must do quickly. He must reenforce the stream wJiile 
it IS at the flood. He must keep the number high by con- 
tinual reenforcement and not wait till the herd is shrinking on 
his hands. 

1 It is needless to remark that many breeders have not yet learned the prin- 
ciple of maintaining their own stock of females ; indeed, a good number confess 
to buying females to " keep up the herd." 



662 PRACTICAL PROBLEMS 

The testing of young females is a difificult business. There 
is Httle use in breeding them to unknown sires, whose own breed- 
ing powers are problematical. To do that is to measure one 
yardstick with another whose standard of accuracy is unknown. 
The young females should be bred whenever possible to tested 
sires, and then the breeder will have an accurate measure of 
what they should be expected to do under herd conditions. 

Unity of the herd. The old plan of having represented in the 
same herd all fashionable families in the person of its females is 
fortunately passing. Such a herd, no matter how excellent or 
well bred its individuals, was after all but a motley collection 
of strongly bred differences, on which no sire ever born could 
be expected to succeed. Such attempts have involved many 
breeders in a hopeless tangle of Mendelism, for these violent 
admixtures of family lines amount to little else than crossing, 
either in theory or in practice. 

The individual breeder succeeds best who attempts to do a 
distinctive thing, and who preserves one type throughout his 
collection of females, which is his herd. He will find this dififi. 
cult enough to accomplish without seeking the multiplication 
of types ; and he will, if he is wise, discard many females in the 
testing, because, if working with well-known and tested strains 
of line-bred stock, one or tzvo tests of a particular combinatioii arc 
as good as a dozen. There is no need that the breeder should 
waste time and money and live in uncertainty if only he will keep 
his type distinct, his blood lines pure, and will test every animal 
that is to have a permanent place in the herd. If he will not do 
this he will indeed be treading a maze of uncertainty, and will 
be ready to say at the end of a long life and as the fruit of his 
experience, "Verily, breeding is a lottery," — an honestly uttered 
but gross libel on one of the greatest professions on earth. 

Testing sires. A well-established herd has always in service a 
mature and well-tested sire who has proved his breeding power 
on some of the best-known females of the herd.^ Not only that, 
but the owner of such a herd is always looking for his successor. 

^ Among the many answers to questions touching this point a surprisingly 
large proportion of breeders confess to testing bulls, not on cows of known breed- 
ing powers but on /leifers. 



ANIMAL BREEDING 663 

If an old and proved sire can be had, that is the sire to buy, 
but ordinarily sires of this kind are not obtainable, for, if they 
are really tested sires, they are usually held in the herd that 
tested them until their period of usefulness is over. If, however, 
one is available, it is a treasure that should not go begging, 
as it often does. If the young breeder would make it a rule to 
buy only old, tested sires, - — though there is no virtue in old 
sires per sc, — he would do better breeding than many another 
with long experience behind him who is constantly accumula- 
ting excellence and as constantly dissipating it by the use of 
untested sires. 

The writer has conducted an extensive correspondence with 
breeders of cattle on this point, and has found that the almost 
universal practice is to buy a young bull, probably a yearling, 
and put him at once into service on tJie entire herd. This is 
business suicide, for it constitutes a bar to any very high degree 
of success and is, besides, extremely dangerous. It is headed 
straight for mediocrity — within the breed of course, but it is 
mediocrity nevertheless. 

Testing young sires. This test, to be most valuable, should 
be made on some of the better females of the herd, whose 
breeding powers are known. It would be folly to use the very 
choicest individuals, for they are needed for more certain work 
with the tested sire at the head ; but something must be known 
about the females on which even the preliminary test is made, 
or it is of little value. 

As all young things look promising, this test will not be 
worth much until the young have neared maturity. To be sure, 
some individuals will be so unpromising as to show it at birth, 
or soon after, but very many mediocre animals will not make 
their mediocrity manifest until maturity approaches. They then 
exhibit their inability to take on the finer finish and the better 
touches that go with the breed. 

On this point experience is full. One of the finest sucking colts 
ever known to the writer was exceedingly perfect as a yearling, 
gave good promise as a two-year-old, commenced to fall away as 
a three-year-old, and before he was five had developed into a 
veritable " pelter " with ewe neck and sway back. 



664 PRACTICAL PROBLEMS 

If the young that are to show the breeding powers of prospec- 
tive sires must reach practical maturity much time will be con- 
sumed in the process. In cattle, for example, the young must 
be not less than one, and preferably they should be at least two, 
years old. Practically a year was consumed in pregnancy, and 
the bull was a year old at the time of service. This will make the 
prospective sire at least four years old by the time his breeding 
powers are actually known. This is the age at which most bulls 
are sold as "ugly and dangerous," a practice which is deplorable. 
All bulls are ugly or dangerous, or both, — that is always to be 
assumed, — but at four years of age they are just ready to enter 
upon the period of real usefulness, and the records will show 
that all great sires have done their work not as yearlings but 
later, after their powers were known. 

Having been tested and proved on a portion of the herd, a sire 
is, of course, placed in full service, and it is but business sense 
to make the most of him as long as he is able to continue at its 
head ; it is even more business sense to begin at once to look 
for his successor. 

A herd without a head. Herds pass quickly, and a herd with- 
out a head is doomed to speedy extinction unless a suitable one 
can be found. A herd in such a condition presents a hard 
problem to the breeder and owner. He has a lot of accumulated 
excellence, but it is liable to die before he can use it unless he 
puts a proper sire at the head without delay. If he cannot do 
that, in all probability dissipation will follow, which is but 
another form of extinction. In this event the only practical 
remedy seems to be dispersion, and this is the real reason for 
more than one of the dispersion sales that come along each year 
to arouse our wonder. 

The dispersion sale affords an exceptional opportunity to 
secure real excellence in breeders, for animals are there offered 
that ordinarily no purchaser could buy, but these sales are not 
necessarily for the best interest of the breed ; in many cases 
it would have been better if the herd could have been kept 
together. 

Tested individuals, male and female, are the backbone of the 
herd, and these are what the wise breeder will preserve through 



ANIMAL BREEDING 665 

all the ups and clowns of his experience. They are his chief 
stock in trade, and he will cherish them as any other business 
man would protect a vested interest. 



SECTION VI — WEATHERING A PERIOD OF DEPRESSION 
AND PRESERVING THE HERD 

No herd can live without ruining its owner unless sales are 
made regularly and at good prices. It is a stream that cannot 
be stopped without damage. 

More than once in the history of most breeds a time comes 
suddenly when for some reason, or for no assignable cause, 
prices drop and matters collapse generally. This calls for all 
the ingenuity of the breeder and all his fortitude in dealing 
with a difficult situation. 

One thing is certain, — the herd viust be reduced. It is simply 
business folly to go on multiplying animals in the face of no 
market. Such a course leads to unmanageable numbers, and 
when they seem to have lost their value no man has the courage 
to do for them what a real breeding herd requires. Under con- 
ditions such as this the herd is doomed to neglect. It is only a 
question of time when their hungry eyes will become a posi- 
tive source of displeasure, if not of disgust, to the owner. No 
one ever looked upon such a herd without a feeling of sorrow, 
for its end is extinction, even though the storm pass and the 
palmy days of the breed return. 

Neither is the other extreme to be advocated, — the dumping 
of everything upon the open market for what it will bring. The 
writer has seen Shorthorns that cost $300 to $500 sold to the 
butcher for $40, to be killed and eaten, only because in sudden 
panic the owners had assumed that the Shorthorns had seen 
their day. 

Now a really excellent breed will never " have its day." If it 
looks that way it means only that the day will come again, and 
not so very far in the future. The breed has served us before 
and it will serve us again, and the man who sells the cream of 
his herd to the butcher or " shoots his horses to feed to the 
hogs," — he is the first man on the ground to restock himself 



666 PRACTICAL PROBLEMS 

at long prices from the herds of those who were wise enough 
to protect themselves and make everything taut while the storm 
might last, but who continued in business against the day when 
the market would again want the produce of their herds. 

When the herd is reduced at such a time, and it must be 
reduced, it is the young and unproved stuff that should be 
sacrificed first, and it is marvelous how much can be sold off 
without disturbing the real ttucleus or producing part of the Jierd. 

If the herd is not all the breeder could desire, such a time is 
the most favorable opportunity that will ever appear to perfect 
the herd by purcJiase. This is the time to gather in the mothers 
and the grandmothers of the breed from other herds, keep them 
out of the butcher's hand, and set them at work ; and about 
the time they have produced another generation, their former 
owners, or other equally anxious purchasers, will be ready to pay 
more for a calf than the tested dam and sire both cost. Every 
one who has lived long among breeders has seen this stampede 
out of the business followed by an equally insane tumble into it. 
The solid breeder will hold himself well together at such a time 
and avail himself of the opportunity both to improve his herd 
and to reap an assured harvest later on. 

SECTION VII — RECORDS 

One of the requirements of all good breeding operations is 
an accurate system of records, covering every important detail, 
leaving nothing to memory. Moreover, the record should be 
made on the spot. 

Herd records. Simple records of all purchases, sales, births, 
and deaths are matters of ordinary business accounts and inven- 
tory, but in addition to these there should be kept what may be 
known as the performance record of the herd. This consists of 
three distinctly separate features : 

I. An accurate description in writing of every individual ani- 
mal of the herd, taken not only at maturity but at birth or time 
of purchase, and as often thereafter as changes in development 
occur. Such a record should be a descriptive history of the in- 
dividual from birth to death, or at least to disposal, accompanied 



ANIMAL BREEDING 667 

by photographs, if possible, and by any measurements, weights, 
achievements, or facts of any kind that may later assist the judg- 
ment in basing conclusions as to selection. The record of the 
service viales should be especially full and complete. 

2. A f.ull description of every individual offspring of every sire 
of the herd as compared with his own description and with that 
of the dam, — such a series of descriptions to constitute the 
breeding record of the sires. 

3. A breeding record should be opened with every female of 
the herd, showing date of service or services, date of birth of all 
offspring, and some name or number which may serve as an 
identification mark for every individual produced, whether living 
or dead. 

If these three lines of data are kept, the breeder will have not 
only an accurate personal description of every animal constitut- 
ing the herd and every one produced by the herd, but he will 
also have a complete breeding record of every animal, both male 
and female, and the two together will show not only how much 
each animal has produced but also what was its quality. When 
breeding operations have been carried on after this plan for a 
number of years, such records will constitute a mine of informa- 
tion which no memory can supply with sufficient accuracy to be 
dependable. Trusting to recollection is dangerous, and the fleet- 
ing impressions formed of certain individuals become rapidly dis- 
torted and unreliable as time passes, — how rapidly no one knows 
until he has been confronted a few times with his own record 
made first hand and upon the spot. These records are essential 
to the best breeding and absolutely indispensable to the man who 
may succeed to the management of the herd later on. 

Breeders too often proceed as if they expected to live forever, 
or at least as long as the herd exists, whereas we must look 
forward to the time when an established herd shall outlast the 
lifetime of its founder, and perhaps two, three, or more genera- 
tions of men shall be involved in shaping the policies of its 
breeding, — all of which is possible only when the most perfect 
records are kept. 

In connection with private herd records the following is 
appended as the plan in actual use by the late Honorable 



668 



PRACTICAL PROBLEMS 



L. H. Kerrick, of Bloomington, Illinois, a very successful 
breeder of the Aberdeen-Angus. These records are kept on 
cardboard 5JL x 8^ inches, and containing no printing whatever. 
They are kept on edge in alphabetical order in a special box, and 
it is but a moment's work to note the present condition of any 
female in the herd ; moreover, every time the owner consults a 
card he is afforded at a glance and involuntarily a picture of 
the complete breeding record of the coiv for her entire lifetime. 
Two records are presented, one of Fair Lady of Verulam and 
the other of her first offspring, Fancy Fair. 

f Ermine Bearer . 1749 
March 21, 1888 Fair Lady of Verulam 

Fancy Fair C. 152 15 



June 20, 1890 

June 18, 1891 
April 18, 1892 
March 25, 1893 
March 12, 1894 
June 15, 1895 
May 2, 1896 
March 15, 1897 
January 27, 1898 
April 6, 1899 
March 30, 1900 
February 12, 1901 
January 17, 1902 



March 18, 



1904 



Wapella Boy B. 1 5094 

Ebon Lizzie C. 16988 

Bunty B. 191 55 

Irene of the Wells . . . C. 21243 
Lucy M. of the Wells. . C. 23451 

Fairie D C. 24961 

Lygia of the Weils . . C. 27945 
Florence F. of the Wells C. 32444 
Erie of the Wells . . . C. 34196 
Senator Hoar of the Wells B. 41949 
Statesman of the Wells . B. 47813 
Bunker of the Wells . . B. 57703 



Florida of the Wells 



9122 <! Fair Lady of Chil- 
ly licothe . . . 2760 
Ellen reagh of 

Kinnoul Park 10203 
C. C. Allen . .11266 
Ebonist . . . 5266 
Ebonist . . . 5266 
Ebonist . . . 5266 
Craigo of Estill . 19518 
Craigo of Estill . 195 18 
Craigo of Estill . 19518 
Willis E. Gray . 24751 
Craft of the Wells 23450 
Craft of the Wells 23450 
CraftoftheWells 23450 
Painstaker of 

Aberlour . . 34220 
C- 75751 Painstaker of 

Aberlour . . 34220 



June 23, 1890 

August 20, 1892 
September 10, 1893 
July 2, 1894 
February 6, 1897 
December 28, 1897 
January 21, 1899 
February 24, 1900 
January 15, 1901 



Fancy Fair 



15215 



Wapella Lady . . . . 

Fair Fancy 

Rose F. of the Wells 

Little Ben 

Operator of the Wells . 
Graymont of the Wells . 
Crouje of the Wells . . 
Miss West of the Wells 



1 699 1 
1 924 1 
36968 
27944 
27962 

32536 

B. 41945 

C. 47809 



Ellenreagh of 
Kinnoul Park 

Fair Lady of 
Verulam . 

H. C. Allen . 

Ebonist . . 

Ebonist . . 

Craigo of Estill 

Willis E. Gray 

Willis E. Gray 

Royal Judge . 

Painstaker of 
Aberlour . . 



10203 

9122 

1 1266 
5266 
5266 
1951S 
24751 
24751 
20371 

34220 



ANIMAL BREEDING 669 

December 16, 1 90 1 Andee of the Wells . . B. 50342 Painstaker of 

Aberlour . . 34220 
November 20, 1902 Castro of the Wells . . B. 57747 Painstaker of 

Aberlour . . 34220 
December2i, 1903 Black Heath of the Wells B. 72985 Painstaker of 

Aberlour . . 34220 
November 27, 1904 Fan-Danof the Wells B. (Castrated) Danwessels of 

the Wells . . 47821 

The plan of the record is simple. It shows that Fair Lady of 
Verulam, born March 21, 1888, was recorded as No. 9122; 
that her sire was Ermine Bearer 1749, and her dam was Fair 
Lady of Chillicothe 2760. It shows that her first calf was 
dropped June 20, 1890, when she was a little over two years of 
age. The C. shows that it was a cow calf. It was named Fancy 
Fair, and recorded as No. 152 15. Her sire was Ellenreagh of 
Kinnoul Park 10203. 

Thus the first name in the first line is that of the cow whose 
record is to be kept. All that follow in her line are her offspring, 
and all the names of the second column are their sires, except 
tJie first tivo. Of these, one (the first) is her own sire, the other 
is her dam.^ 

In transmitting these data Mr. Kerrick observed : 

You will see that whenever I am so inclined, I can commence with the 
letter A and lift up these cards in order until the right one appears. 
Instantly, when I lift a card, the life performance of a cow is shown. It 
does not take long to go through a large herd and see just what each cow 
is doing. If I find a number of cows not showing a calf reasonably near 
the date at which I am looking through the cards, we can make a note in 
each case. 

It would be interesting to you to see what this one cow. Fair Lady of 
Verulam, has done. If a 22-year-old boy would luckily buy three such 
cows, he would have a fine big herd at 32, and after that all the cattle he 
would want. On the other hand, with a couple of shy-breeding things, and 
they bringing mostly bulls, he might not have any more at 32 than when he 
started in the business. A big part of our herd to-day (numbering over 
300) are descendants of Fair Lady of Verulam. 

These cards might well be extended to cover other details, 
especially as to whether the offspring is retained in the herd or 
sokl, and, if sold, to whom and at what price. 

^ On the back of these cards is an outline for an extended pedigree. 



670 PRACTICAL PROBl-EMS 

This latter point is covered in the system in use by A. J. Love- 
joy, of Roscoe, lUinois, a well-known breeder of Berkshires, a 
sample card from whose herd is here reproduced : 

Index No. 16. Imported Bessie II 55101, farrowed April 10 to Master- 
piece 77000. Farrowed 5, saved 5 : boars 4, sow i 

Sold boar to J. W. Martin, Gotham, Wisconsin #150.00 

" " " L. W. Brown, Berlin, Illinois 75-oo 

" " " J. R. Logan, Seward, Illinois 50.00 

" " " Hibbard & Brown, Michigan 125.00 

" sow " Nebraska Insane Hospital, Lincoln, Nebraska . . . 50.00 
Total for litter of 1905 #450.00 

In connection with office records of this kind the "breeding 
book" kept at the barn should record the date of every service, 
the date, sex, and any distinguishing fact concerning the birth 
of every individual, living or dead, and any other fact that would 
prove of the slightest value in estimating what the herd is doing 
or has done. 

If, then, in addition, there were kept an accurate " descriptive 
record " of every individual that is considered worthy to enter 
the herd, or to be sold as a breeder, and besides this also as ac- 
curate a record of the JinwortJiy pj'odiicts of the herd, the breeder 
would have — not only for his own satisfaction and profit when 
memory fails or becomes confused, but for that of others who 
may handle his breeding — a record of qualities good and bad 
on which a skillful breeder can safely base his selection. With- 
out a record such as this all real selection is limited to what is 
done with the eyes on animals still living, except as a man may 
be guided by an uncertain memory. How uncertain that is he 
will realize when he revisits in full prime of life the hills and 
valleys of his boyhood. 

Pedigree records. That which is needed within the herd is 
equally important within the breed. The facts of heredity go 
to show that all good breeding requires that the type shall be 
unchanged for at least six generations, if we hope to get any- 
thing like uniformity of offspring. If this be true, we need 
accurate records covering all important details and all valuable 
characters for at least the six generations required to produce 
a stable type. 



ANIMAL BREEDING 67 I 

Now our pedigree records furnish little information outside of 
blood lines, and they are totally silent as to what the individuals 
actually were in their own personalities. This information the 
breeder needs and must have if he is to succeed. Some slight 
beginning has been made in the way of track records among 
racing horses, and in advanced registry among dairy cows. 
Then, too, breeders aim to supply in their private catalogues 
some detailed information about particular animals ; but in many 
cases such description contains so large an element of adver- 
tising as to throw doubt upon its accuracy. 

As the case stands to-day, there is no way in which an impar- 
tial and trustworthy record can be assured even of our most 
famous and valuable animals. This being the case, the individual 
breeder coming into the business must devote years of his life 
to the accumulation of a mass of data more or less reliable, 
gathered irregularly and often surreptitiously from the under- 
current of side talk in which old and prominent breeders, like 
other mortals, sometimes indulge. 

Now this ought not to be. Such information belongs to the 
breed and to future breeders, who have a right to know the facts 
about the animals whose blood lines they are obliged to use ; and 
sometime, in some way, when commercial interests are no longer 
supreme, — if not before, — an accurate and impartial descrip- 
tion of every great animal will be made a matter of permanent 
record and will find its way into the history of the breed. 

It is to the interest of the breed that this should be so, and it 
is also to the interest of the young breeder, that he may proceed 
at once and intelligently with his breeding operations and not 
spend twenty of the best years of his life in collecting informa- 
tion by indirect and often devious methods, — information that 
is by good rights public property, and as such is the rightful 
heritage of every man from the moment he becomes a breeder 
of that particular breed. 

A brilliant future awaits the breed that will secure and put 
into its history an accurate and critical description, at least of 
every famous animal, said description covering all distinguishing 
or unusual traits both desirable and undesirable, and not confined 
to extravagant praise. 



672 PRACTICAL PROBLEMS 

If this is ever to be clone, some feasible plan must be devised. 
Now in this matter two things are self-evident : first, such tnttJi- 
fnl and critical description could not be made, or at least made 
public, during the lifetime of the animal, while large commercial 
interests were involved ; and second, more than one man's judg- 
ment should be consulted in making the actual record. 

The writer ventures to suggest that while the animal lives, 
and is in his prime, and while his character and achievements 
are well known, a full statement of his achievements be made 
and two critical descriptions be prepared, one by the owner, 
the other by a committee of the association, — all to find a per- 
manent place in the published records of the breed. 

How this object can be achieved is problematical, but until it 
can be achieved, the best results in animal breeding will never 
be possible. One thing is certain, — the public at large and the 
association of breeders in particular have an inherent, if not a 
vested right, in every animal that comes prominently before the 
public, and sometime, in some way, this larger right of public 
ownership will be conceded greatly to the general interests of 
the breed and to the convenience of future breeders ; in other 
words, not even private commercial interests will always inter- 
vene to prevent a record of the facts, until, by the death of all 
parties possessing actual knowledge, the real personality of a 
famous animal has become lost beyond the power of restoration. 

The blood of not only one famous animal but of many famous 
animals runs through the pedigrees of all our herds. The fame 
of some of them rested on real excellence and well-earned merit ; 
that of others was due chiefly to skillful management, often to 
shrewd advertising. Animals of both classes possessed points 
of high excellence, and both classes also possessed defects. The 
public has a right to \\\c facts ^ which are no less than a vested 
interest to every man who owns a breeding herd. 

SECTION VIII — DISPOSAL OF SURPLUS FEMALES 

The herd itself must make the first draft upon its female 
output in order to secure material to reenforce its numbers. 
Some females will be needed by other breeders of standing to 



ANIMAL BREEDING 673 

replenish or extend their herds. What shall be done with the 
rest ? The answer to this question depends somewhat upon the 
class of animals and the circumstances of the breeder, but on 
general principles the destination of surplus females should be 
the open 'market, and this destination should be reached as 
soon as possible after unfitness to take a place in the permanent 
herd is well established. 

The one thing that should not be done is to employ this 
surplus generally as material for the establishment of new herds. 
There is a feeling among breeders that no animal eligible to 
registry should be sent to the open market, especially to the 
shambles. Nothing could be more erroneous. To use surplus 
females for the estabhshment of a multitude of small, weak 
herds in the hands of men who have no experience and no 
genius for breeding, is at first to arouse vain hopes that will not 
be realized and afterward to bring down curses not only on 
"blooded stock" and breeders in general but on this special 
breed in particular. 

The safest and the best destination of all surplus females is 
the open market, where they will sell for what they are worth 
and be entirely safe and out of the way, with a small but safe 
balance to their account on the books at home, after having 
afforded the best possible practical test of the real commercial 
value of the type that is being bred in the herd which they 
represent. In this way all females help to test the herd. 

SECTION IX — A MARKET FOR SIRES 

It is quite the opposite with males. The great business of 
all pure-bred herds is the production of sires, and the country 
ought to be industriously campaigned in the interest of " placing " 
sires for grading purposes. If they cannot be sold let them be 
rented, or in some way gotten at work. Let there be coopera- 
tion between breeders, even between breeds, for the placing of 
sires. Let salesmen cover the country as do agents of machinery, 
and sell sires on some terms. The practice of grading must 
be brought into American farming, and nobody is so much 
interested in this as the breeders themselves. The common 



674 PRACTICAL PROBLEMS 

stock needs the sires for the service, and the breeders need 
the market. 

Breeders are selhng too much back and forth among them- 
selves. The breeding business is too much of a mutual benefit 
association, while there is an undeveloped public with almost 
unlimited buying powers, that needs to be educated and its 
buying powers developed. Many a breeder works industriously 
to sell two or three females and a sire to a novice, partly for the 
money that is in the sale and partly to spread the gospel of 
better breeding, as he thinks. 

It does not work that way. A novice has been started in a 
small business. The chances are great that he will not succeed. 
He will either fail and curse the breed, or succeed only indif- 
ferently well and make an undesirable competitor who is willing 
to sell stock of the "same breeding" at prices much below 
what they must cost when produced by careful breeding. 

If the same man had bought a sire he would have been satis- 
fied with the new breed, and he would be on the road to a perma- 
nent habit of keeping better live stock. Me would then become a 
customer again and again. From any point of view the breeders 
must develop the market for sires for grading purposes. 

SECTION X — COMMUNITY BREEDING 

Many advantages will follow if an entire community will go 
into the production of a particular class of animals, as, for 
example, driving horses. There are a thousand little details in 
the successful management of any business, and for the best 
success, mind must react upon mind. If a whole community 
would go into the production of driving horses and discuss the 
driver, his breeding, care, development, and education, as com- 
munities now discuss corn raising in the corn belt, in a few 
years every man, woman, and child in that particular locality 
would "know all about horses." They would soon become 
skillful drivers, and, as is now the case in the famous blue-grass 
region of Kentucky, the community would have a reputation 
that would attract buyers, and a horse would bring more money 
than he could bring if he were the only one in the neighborhood. 



ANIMAL BREEDING 675 

Let the whole community, as far as possible, breed the same 
kind of horse or other animal, so that it may win a reputation 
for a distinctive product, and it will not only do better breeding 
than it would if it were to breed many types, but the business 
will be vastly more profitable. Practically all the canaries of 
the world are bred in two villages in Germany, and no bird with 
a false note is ever allowed to live, so skilled have the entire 
village become in what might be called canary excellence. No 
individual breeder can ever equal the degree of success which 
is here evolved, where practically no other interest engages 
the attention of the community. 

SECTION XI — THE YOUNG BREEDER 

There is no reason why the young breeder should not possess 
himself thoroughly and quickly with the principles of breeding. 
What he lacks is experience with animals and real information 
about breeds. He should get his experience either by grading 
or by association with a good herd, but he must needs pick up 
his information, much of it at least, from intimate association 
with men who are in the active business of breeding. 

The " sucker" in the sales ring. Above all, the young breeder 
must keep his head. He does not need and Jie cannot afford to 
pay large prices for females. If he sees some old and established 
breeder bidding high on a young female, he must not assume that 
he can afford to bid equally high. There are a dozen reasons 
why the older breeder may want that particular animal, none of 
which would apply to the young breeder. For example, it may 
be the only one of that particular breeding outside the herd of 
the older breeder, and he can perhaps, or thinks he can, afford 
to pay even more than the animal is worth for the sake of con- 
trolling that particular combination ; or he may want it to put 
into the show ring, or to mate with a particular sire. None of 
these reasons would apply to the young breeder, who, if he buys 
it, takes it for its merit. 

The best way for a young breeder to get his start in pure-bred 
animals is to get it from a reputable breeder who can be persuaded 
to sell some really excellent and tested, or partially tested, females. 



676 PRACTICAL PROBLEMS 

It is doing no injustice to any breed to remind the young 
breeder that the bulk of young things come to very Httle. He 
will be safer with old animals — even those of considerable age, 
providing they are still fertile. 

With him much depends upon price. He has no call to pay 
extreme prices. He cannot sell his stuff at maximum prices till 
he has been in the business long enough to acquire something 
of a reputation, and one of his best early reputations is as a 
careful, judicious buyer. 

If the young breeder ever loses his head in the sales ring, let 
him not do it on a female, that can at best produce but few, or 
upon extremely young things, which stand about as many chances 
of coming out wrong as they do of coming out right. 

ADDITIONAL REFERENCES 

Animal Breeding. By W. M. Hays. Breeders' Gazette, XLV, 199, 
252, 3o5> 356, 461, 513, 565, 608. 

Breeding Bees to increase Length of Tongue. By |. M. Rankin. 
Michigan Experiment Station Report, 1897, p. 127 ; also in Experiment 
Station Record, XL 61, 1062. 

Breeding Experiments with Sheep. Missouri Experiment Station, 
Bulletin No. 53, pp. 167-188; also in Experiment Station Record, 
XIV, 383. 

Breeding Poultry. Experiment Station Record, XIH, 176. 

Breeding Poultry for Egg Production. By G. M. Gowell. Maine 
Experiment Station, Bulletin No. 79; No. 93, pp. 69-92; also in 
Experiment Station Record, XV, 394. 

Breeding Sheep to change Breeding Season. By T. Shaw. Min- 
nesota Experiment Station, Bulletin No. 78, pp. 71-87. 

Cross-Breeding Chickens. By E. P. Miles. Virginia Experiment Station, 
Bulletin No. 96, p. 6 ; also in Experiment Station Report, XL 1074. 

Cross-Breeding Sheep. By F. Winter. Agricultural Gazette, London, 
1900, p. 246. 

Cross-Breeding Swine. Experiment Station Record, XL 1077. 

Crossing Cattle. Experiment Station Report, VIH, 720. 

Hybrid, Gamecock-Guinea-Fowl. By T. Vilaro. Bulletin of the 
American Museum of Natural History, 1897, p. 225 ; also in Experi- 
ment Station Record, IX, 1031. 

Pedigree Stock Records. (Report of Committee on Photographic 
Methods of Preserving.) By Francis Galton. Report of the British 
Association for the Advancement of Science, 1899, pp. 424-429. 



CHAPTER XXI 

DEVELOPMENT 

Thremmatology is interested in growth as well as in reproduc- 
tion ; in the proper development of valuable characters as well 
as in their transmission and inheritance. 

What an individual comes to be at maturity is a kind of result- 
ant of the characters born into him and the opportunities for 
their development afforded by the conditions of life. While the 
surroundings during development cannot in any sense compen- 
sate for deficiency in inheritance, the opposite is also true, that 
the richest heritage is fruitless of results if conditions of life 
make their development impossible. 

External conditions only indirectly causes of variation. Con- 
ditions external to the organism thus operate only iiidircctly as 
causes of variation. Their good results depend entirely upon the 
capacity on the part of the individual or the breed to avail itself 
of their advantages, and this capacity is born into the organism 
or it does not possess it, — it cannot be implanted from without. 
That is to say, no amount of feeding would make draft horses 
out of those that are racing bred, or beef cattle out of those 
bred for the dairy, and it would be a great waste of feed to try 
it. Certain experiments with individual animals, it is true, seem 
to teach that Jerseys, for example, are successful feeders. Such 
experiments will deceive no one who realizes the full extent of 
variability in all breeds, and that individuals can be found to 
prove almost anything. When some adventurous investigator will 
take the trouble to feed off three hundred Jerseys against three 
hundred Shorthorns, and work out the mean and the standard 
deviation for both, then he will learn that a breed cannot be 
selected for unknown generations for milk only, and still retain 
or attain meat-producing powers equal to those of a breed 
selected almost exclusively for that purpose. If it could, there 
is little in selection and less in breeding, and the wonder is that 

677 



678 PRACTICAL PROBLEMS 

anybody ever seriously doubted this fact. This is altogether 
outside the question of the " dual purpose " animal, for no 
attempt has been made to breed the Jersey for other purposes 
than milk production. Nor is it a reproach to Jerseys that they 
do not excel in something for which they have never been bred. 
As well expect them to take records upon the race track, or to do 
any other thing for which they have not been fitted by selection. 

The influence of the environment is therefore permissive 
rather than assertive. It affords the material and the opportu- 
nity for development of what was born into the individual, and 
what was not born into it cannot develop, no matter how favor- 
able the environment, — as witness the very different develop- 
ment of two individuals differently born but living under the 
same conditions of life. If an individual is exceptional, we may 
say of him with confidence that he was both well born and well 
conditioned during development. If, on the other hand, he is 
inferior, we are uncertain whether to attribute it to non-inherit- 
ance of valuable characters, or to their failure to develop owing 
to unfortunate conditions, or to both. 

Well-bred individuals should have good conditions. It is mani- 
festly unwise to expend time, money, and thought on the pro- 
duction of individuals highly endowed with the richest possibilities 
of the race and then fail to provide the necessary conditions for 
their development. Ordinary business sense, therefore, dictates 
that the breeder should secure ideal conditions for the full and 
proper development of the characters whose improvement he 
aims to secure through fortunate combinations of blood lines. 
To see herds of the best-bred animals suffering for feed is at 
once pathetic from the humanitarian standpoint and unaccount- 
able from a business standpoint. 

Having spent time and money for the infusion of the highest 
possibilities into the herd, certainly business foresight demands 
that their full realization shall be prevented by no ordinary cir- 
cumstance ; yet what share of the best-bred animals and what 
proportion of our improved seeds are given full opportunity to 
show what is really in them .? 

The breeder is interested for another reason in securing the 
full development of all that is born into individuals and family 



DEVELOPMENT 679 

lines. In no other way can he judge of their real excellence and 
in no other way is his selection safe. The practice of fitting for 
the show ring is often deplored, and not without good reason, 
but of one thing we may be well assured, — we can never be 
certain of the capacities of an individual until they have been 
put to the test by development. 

One of the hard facts of animal breeding is that the develop- 
ment of young things is very often left to men who are not 
skilled in animal production. They seem to assume that the 
well-bred animal in some way can get along under less favorable 
conditions than can the unimproved, — a kind of offsetting of 
breeding against feeding and care. 

Improvement consists in producing animals and plants able to 
make good returns for good conditions, not merely to exist under 
hard conditions. This fact ought to be pasted in the hat of 
every farmer. The purpose of breeders is not to produce strains 
that can live on next to nothing, and that are able to endure 
hard conditions and not die outright ; it is to produce strains of 
animals and plants that are able to make good returns for the 
fuller feed and better care which the civilized and educated 
farmer can give as compared with nature, which is capricious, 
or with the unskillful semi-savage, who is improvident. 

One of the most serious faults of unimproved strains is that 
they do not respond to better food or to more of it. They have 
been selected for generations for their powers of resistance to 
hard conditions, and that is where their strength lies. Now that 
we can provide better food, we need animals of higher efficiency ; 
indeed, that is our argument for better animals. Then, again, 
having animals of higher efficiency, we need better feed and 
more of it, and that is our argument for better-bred corn and 
other crops. So the tw^o — animal breeding and better feeding 
— react the one upon the other, and both go with better farming 
and with the greater needs of an advancing civilization. 

The well-bred animal is a high-class machine. This fact can- 
not be too well understood by every man who comes into relations 
with the well-bred animal, and it is true, whether we consider 
animals as machines for the producing of milk or meat, of labor, 
or of body covering ; whether we consider that they are to 



68o PRACTICAL PROBLEMS 

minister to our necessities or to cater to our enjoyment by 
personal service, as with the saddler and the driving horse. 

Excellence is not to be measured by the power to withstand 
deprivation, but rather by efficiency to do work under full feed 
and under good conditions ; and to this end it is but good busi- 
ness sense to secure for each individual the full development of 
all the useful qualities with which he is naturally endowed. 

Development is a study by itself. Here is an entire field 
almost unexplored. We know, in a general way, that the 
"energy of embryonic development" is never attained later in 
life, and that if we would secure full development in growth we 
must ** keep the young thing growing." In some way or other 
this business of body development, if once checked, is never 
again fully resumed. It is true that a few experts have learned 
fairly well how to develop speed in horses, and others how to 
train saddlers and drivers ; but wJietJier we consider the growth 
of the body, the development of its functions, or the education of 
the mental faculties, zve do not yet possess even the rudiments of 
the knozv ledge of the most successful development. With us only 
an occasional individual enjoys optimum conditions throughout 
his life, and only a few exhibit in their own personality the really 
wonderful capacity of the breed to which they belong. If one 
were to say that the science and practice of breeding is far better 
known than that of development afterward, he would be well 
within the truth, and in the opinion of the writer here will lie 
some of our greatest improvements of the near future. The 
excessive fitting of an occasional individual for the show ring, 
regardless of consequences afterward, is not what is here meant, 
but rather the orderly and full development, in substantially all 
individuals, of those qualities which we deem valuable, so that 
we may fully realize in our animals the qualities we select and 
breed for in our yards. 



APPENDIX 



STATISTICAL METHODS 

By H. L. RIETZ, Ph.D. 

Assisiani Professor of Mathematics, University of Illinois 

SECTION I — INTRODUCTION 

An elementary account of the mathematical theory of statistics in a 
treatise on Thremmatology needs no justification after the foregoing text. 
The doctrines of evolution and heredity rest on a statistical basis, ^ because 
we are, in general, concerned with groups of individuals, and with occur- 
rences of such a nature that, although we cannot make definite quantitative 
statements about any one of them taken singly, we can make statements 
in regard to a large number of them taken together with a degree of cer- 
tainty which increases as the number increases. For example, a thousand 
ears of corn may vary in length from three inches to eleven inches and 
have an average (average to be defined in Section II) length of 8.5 inches. 
We cannot state with any degree of certainty the length of an ear selected 
at random out of this group of a thousand ears ; but if we select at random 
five hundred ears out of the thousand we can assert with considerable confi- 
dence that the average length of the five hundred ears will differ but little 
from 8.5 inches. 

The important questions in every case are the.se: In what way can we 
best describe a population whose variates we have measured ? How can 
we give the meaning and information contained in this mass of figures in 
a few words or symbols ? 

A glance at the figures may give a personal impression, but this is not 
reliable, as is proved by the fact that two persons may each get a very 
different personal impression, even when examining the same set of figures. 
We must here resort to more exact methods, and it is the object of this 
appendix to present in a brief and elementary manner the mathematical 
methods of deahng with such masses of figures. 

SECTION II — AVERAGES 

Meaning and function of an average. The fundamental questions which 
arise in the discussion of averages are: (i) What is meant by "the aver- 
age of a system of variates " .? (2) Why do we make use of averages at 

1 See Karl Pearson, Grammar of Science. 
681 



682 APPENDIX" 

all ? (3) What are the objects of having different kinds of averages ? 
Such questions as these are apt to be overlooked by those who have formed 
the habit of averaging all kinds of results without careful thought. 

In popular language, we speak of the average daily temperature, the 
average length of ears of corn, the average student, the average citizen ; 
and we should know the exact meaning to be conveyed by these and simi- 
lar expressions before using them in scientific discourse. 

The taking of an average presupposes a population whose variates have 
a certain measurable character about which we are concerned, and that 
the measurement of this character differs in different individuals. We 
attempt to describe this population by putting aside the rtieasurements of 
individuals and constructing a single intermediate number which shall be 
descriptive of the total population, in so far as one number can describe 
a population. 

The single intermediate number which answers this purpose is, in the 
general sense, some kind of an average. We thus use averages for descrip- 
tive purposes in the interest of brevity ; but, taken alone, an average can- 
not completely describe a population any more than the motion of the 
center of gravity of a system of material particles can completely describe 
the motion of the separate particles. 

In stating what an average is we have also stated its function ; but, as 
just indicated, it must not be assumed that an average gives all the infor- 
mation which is to be secured from the measurement of a population. It 
can only take the place of the mass of figures for certain special purposes. 
In fact, there has been a tendency, by somewhat careless workers with 
statistical data, to attach too much importance to averages and not enough 
to deviations from the average, — a point that will be dealt with in a later 
section. 

There are five different kinds of averages in common use for different 
purposes. These are (1) the arithmetic mean, (2) the weighted arithmetic 
mean, (3) the geometric mean, (4) the mode, (5) the median. 

While some of these averages have been defined, and used freely in the 
text, it seems well to restate these definitions together with the others, the 
better to discuss their respective advantages and disadvantages, and some 
of the purposes to which each is adapted. 

The arithmetic mean. The arithmetic mean of a population of n variates 

may be defined as follows: 

sttin of iiieasjirement of n variates 

arithmetic mean = 

11 

That is, to find the arithmetic mean of n variates, we divide the sum of the 
measurements of these variates by the number of variates. 

Thus, in the case of a thousand ears of corn, the arithmetic mean of the 
lengths of the ears is the sum of the lengths of 1000 ears divided by 1000. 
The use of this kind of an average has always been taken by observers as the 
best method of combining direct measurements of the same quantity. This is 



APPENDIX 



683 



the average most commonly employed, and one of the strongest arguments 
advanced to justify this method is its universal acceptance. It is worth 
while, however, to call attention to one of the abuses of the arithmetic 
mean. For instance, if a very few (say four) measurements have been 
made of a certain character, the arithmetic mean has often been taken as 
a good index of their meaning ; but if these few measurements differ 
widely, to report their arithmetic mean is to furnish a very misleading and 
untrustworthy piece of information. This has often been done by those \ 
who have given no thought to statistical methods. 

There is a sort of commercial point involved in the arithmetic mean 
which should not be overlooked. For instance, if a real estate dealer sells 
a hundred lots at various prices, of which the arithmetical average is $800, 
this assures us that if the seller had sold each of the lots for #800, instead 
of selling at different prices, he would have realized precisely the same 
from the sale of the whole number of lots as he has realized from selling 
at varying rates, even though we have no information as to what any indi- 
vidual has paid for a lot. 

Weighted arithmetic mean. A slight modification of the above method 
is often used. To illustrate, the thousand measurements of lengths of ears 
of corn may be arranged, let us say, in half-inch groups as follows : 



Inches .... 


3-0 


3-5 


4.0 


4-5 


S.o 


5-5 


6.0 


6-5 


7.0 


7-5 


8.0 


8.5 


9.0 


9-5 


lO.O 


10.5 1 II.O 


II. 3 


Frequencies . . 


5 


6 


13 


17 


18 


55 


61 


73 


80 gS 


113 


134 


142 


100 


53 


26 


5 


I 



where, for instance, the 6-inch group includes all ears whose lengths are 
between 5.75 and 6.25. In general, if t'j, 7',,, . . ., 7/^ represent the class marks, 
andyj,y2' ' ' 'ifr represent the corresponding frequencies, then 

weighted arithmetic mean — -^^ ^ — /2_2 y^r ^ 

/1+/2 + •••+/- 

Stated in words, this mean is obtained by iiniltiplying eacli mark of a 
class by the corresponding frequency^ and dividing the sum of the products 
by the total population. 

This kind of average is used a great deal in our work and is approxi- 
mately equal to the ordinary arithmetical average if the groups are fairly 
narrow. Its advantage over the ordinary arithmetic mean lies in the fact 
that it is more easily computed. In reporting the mean daily temperature, 
the average length of ears of corn, the average height of a certain class of 
men, one of the above kinds of averages is meant. We use these averages 
so much in this work that we speak of them as " the mean," for brevity, 
so that when the term " mean " is used without a limiting adjective, it is to 
be understood that an arithmetic mean is meant. 

The geometric mean. The geometric mean of n members is found by mul- 
tiplying the numbers together and extracting the nth root of the product. 



684 



APPENDIX 



Let us assume that during a decade the attendance at a university in- 
creased loo per cent, and let us propose the problem of finding the average 
annual rate of increase. Will it do to resort to the arithmetic mean in 
this case and say that the average rate of increase is lo per cent ? No ; an 
increase of lo per cent annually would give an attendance (i.io)^**= 2.59 
times the attendance at the beginning of the decade. What we really want 
is V2 = 1.07 + ; that is, an increase of a little more than 7 per cent each 
year will double the population in a decade. 

The geometrical average is but little used in our work, but it is brought 
forward here to remind us that an average can, in general, be depended 
upon only to serve a definite purpose ; and, when the purpose is known, we 
are sometimes confined to one kind of average, or at least able to see the 
advantage of one kind of average over another. Suppose that we know the 
protein content of corn to have been increased 50 per cent in ten years' 
breeding. Can we say that the average annual rate of increase was 5 per 
cent .'' Clearly we cannot. What we should do is to take 



V7 



50 — I. GO = 0.041 



and say that the average annual rate of increase is approximately 4 per cent. 

The mode. When we speak of the average college student or the aver- 
age citizen we certainly do not have reference to the arithmetic or geo- 
metric average of anything. When we say a man is an average citizen 
we mean that he represents a type which is met oftener than any other. 

If a community has ten millionaires, but all the other citizens are in pov- 
erty, an arithmetical average might give the impression that the people of 
the community are in good financial condition, while really the " average 
citizen " is in poverty. The averages thus far discussed are in no way 
suited to describe this population, but the average called the " mode " is 
useful for this purpose. 

If a population be arranged in seriate order with respect to some char- 
acter, a mode is a value to which there corresponds a greater frequency 
than to values just preceding and immediately following it in the arrange- 
ment. A population may have more than one mode, but the populations 
with which we shall deal have, in general, only one. 

This kind of average seems to be about the same as that of the news- 
papers when they speak of the average citizen. In a democracy we often 
hear the cry of " the greatest good for the greatest number," and insist that 
legislation shall benefit the average man, — the man at the mode. 

Reverting again to the thousand ears of corn arranged in half-inch groups, 
it should be noted that the frequency increases up to the cla.ss of mark 
9 inches and then decreases. We might conclude that 9 inches is exactly 
the mode for this population. It must be remembered that all measure- 
ments from 8.75 to 9.25 inches were placed in the 9-inch group, and that 
a different grouping might change the frequencies somewhat. Hence 9 is 
said to be the empirical mode, and the tJieoretical mode is defined as a 



APPENDIX 685 

point of greatest frequency of the theoretical distribution, of wliicli the 
given distribution is a sample. As a disadvantage, it should be mentioned 
that it is somewhat difficult to determine the theoretical mode accurately. 
It may also be pointed out that for a very irregular group of figures the 
mode is practically useless. Its great service is to characterize a type, and 
with a very irregular group of figures the existence of a type is not mani- 
fest ; indeed, a type may not exist. 

The median. If all the variates are arranged in serial order, the value 
corresponding to the middle variate is called the median of the population. 
Thus, if we should speak of the wages of a thousand and one laborers, we 
should mean by the median the wages of the middlemost of these men 
when they are arranged in serial order with respect to wages; that is, if 
five hundred received less than #1.72, and five hundred received more than 
#1.72, we should say that ;?i.72 is the median wage. The median has the 
great advantage that it can be easily determined. Very large and very 
small values do not affect it. It is only a question of being above or below 
the middle in an arrangement. Its great disadvantages are that it may be 
totally removed from the type and that it gives no special importance to 
extreme values. 

Averages of whatever kind are designed to exhibit the main features of 
a population by means of a few well-chosen numbers. We have seen that 
the particular average selected depends upon the purpose we have in view. 
Now, if this purpose is merely one of comparison between two similar 
groups, then almost any kind of an average will do. The ordinary and the 
weighted means have been used for the most part in this work, but con- 
ditions may easily arise where some other average is more suitable. Bowley 
has well stated the following as the characteristics of a good and suitable 
average : " If there is a type, it shows it ; it gives due influence to extreme 
cases ; it is not easily affected by errors, or much displaced by slight 
alterations in the system of calculations ; and it is easily calculated." 

It is often useful to give more than one average in order to describe a 
population ; for the relative positions of the mean, the mode, and the median 
give a good deal more information about the distribution of a population 
than any single average can give. For a great many distributions Pearson 
has found an approximate relation to exist between the mean, the mode, 
and the median. This relation is 

theoretical mode = mean — 3 (mean — median). 

It is, of course, possible to form fictitious frequency distributions for 
which this relation does not hold, but it is important as indicating what 
nature, in general, provides. 

The use of averages for representing what is often spoken of as 
the " true value " can be better discussed in the section devoted to the 
probable error. 



686 



APPENDIX 



SECTION III — GRAPHIC REPRESENTATION OF 
STATISTICS 

A mere tabulation of any considerable number of figures does not make 
it possible, in general, for the mind to grasp the main facts which the 
figures represent ; in fact, such a tabulation of, say a thousand figures, may 
make no impression on the mind which is at all worth mentioning. By the 
graphic method, however, the chief characteristics of a mass of figures are 
presented to the eye by means of a picture or curve. The graph gives, 
at a glance, important facts which may be overlooked, or which can be 
obtained from the figures only by considerable labor. 

The use of graphic methods in statistics is very extensive, and has proved 
to be of great .service. In fact, everyone who has to deal with complicated 
groups of figures comes to appreciate the graphic method, as it enables one 
to perceive relations through the eye. 

It is the object of this section to show how graphs are formed from given 
data. 

Frequency curves. Let us consider the graph of the following frequency 
distribution, in which the first line of the table gives the marks of the 
classes, and the second gives the number of variates in the classes : 





'Values 


4.0 


4-5 


5-0 


5-5 


6.0 


6.5 


7.0 


7-5 


8.0 


8.5 


g.o 


9-5 


lO.O 


Frequencies .... 


I 


I 


8 


33 


70 


no 


176 


172 


124 


6i 


32 


10 


2 





What we propose to do here is to present a significant picture of this 
population. 

Draw two lines, OX and 01^ at right angles to each other (Fig. i). 
These reference lines are called coordinate axes. The line OX is called 
the .t'-axis, and the line 6> F the j-axis. The point O, from which we meas- 
ure, is called the origin, or zero point. Beginning at this point mark off 
on the ,r-axis equal intervals upon a scale convenient to the problem at 
hand. From the same zero point lay off equal intervals also on the /-axis. 
These need not be on the same scale as those on the .I'-axis, but should 
be suited to best bring out the facts to be shown by the graph. Not all 
graphs are drawn upon the same scale therefore, nor are the two axes of 
the same graph alike as to spacing or scale. 

In the particular case in hand, let each interval along OX represent a 
half inch. The question as to what each interval shall represent is a matter 
of the scale used ; and the scale must be chosen to suit the particular data 
in hand. Next, along C^.V lay off the class marks. Corresponding to each 
class mark there is a frequency. From the various points on the .i-axis 

1 This distribution is taken as a representative of any frequency distribution. It is not, 
however, made up artificially, but actually represents the distribution of eight hundred ears 
of corn with respect to length. 



APPENDIX 



687 



which represent class marks lay off lines parallel to the ^-axis and of 
lengths corresponding to the various frequencies, according to the scale on 
the _y-axis. When this is done there will be a series of parallel lines at 
equal distances apart, all perpendicular to the jf-axis and parallel to the 
_y-axis, but of lengths corresponding to the various frequencies and therefore 
unequal. Joining the tops of the lines so constructed by straight lines 
gives the, frequency polygon sho^fn in Fig. I. The tops of the lines thus 
joined give an orderly arrangement of points, through which it may be 
possible to draw a smooth curve. If it is impossible to draw a smooth curve 
through all of them, draw a smooth curve as near as possible to all of them. 
The curve so drawn is called ■&. frequency curiae (not shown in figure). 



200 
















C' E 


160 






I 


\ 


U'U 




B 




C 


\ 


8U 


-jP 




' 




\ 


40 










\ 








A 


B 


F \. 



8.5 9 y.5 10 



Fig. I 



Any point P in the plane represents two numbers : the one number is 
represented by the distance of the point from the_y-axis, and the other by 
its distance from the x-axis. The number which gives the distance of P from 
thej-axis is called the abscissa of P, and the number which gives its distance 
from the .r-axis is called its ordinate. The two numbers together are often 
spoken of as the coordinates of the point P. 

Significance of area under curve. Construct rectangles such as ABCD 
and BC'EF on the ordinates at class marks as mid-lines, making the sides 
AD, BC, etc., bisect the class intervals along the a-axis. Suppose, now, 
that we define unit area as a rectangle bounded by AB, AD, BC, and a 
line parallel to AB and just far enough from it so that the distance 
between AB and this line represents unit frequency. Then the area of 
ABCD is no, and the area of all such rectangles taken together is equal 
numerically to the total population. In drawing the smooth curve men- 
tioned above, we should aim to make the area between the curve the 



688 



APPENDIX 



.r-axis, and the two end ordinates (in this case ordinates at 4 and 10) equal 
to the sum of the areas of these rectangles. The area under the curve 
then represents the total population. This is an important point, because 
it presents to the eye how much of the population is included between any 
two measurements. For instance, at a glance you could estimate approxi- 
mately the portion of the population discussed in Fig. i, whose measure- 
ments are between 5 and 8. The use of the area under the frequency curve 
will be found helpful in our discussion of "probable error." 

Choice of scale. In drawing a graph the question always arises as to 
what scale shall be used in plotting, but unfortunately no definite rule can 
be laid down. It may, however, prove useful to call attention to a few 
points. First, we should choose such a scale that we can plot all the points 
on one page of the paper used ; for it is a great advantage to have the 
whole graph on one paper, thus making it visible to the eye in its entirety. 
Second, if the point involved in the investigation is a question of rate of 
increase or decrease, we should select such a scale as to make the curve 
reasonably steep. Frequency curves are used a great deal in the study of the 
social sciences, as well as in natural science. For instance, the sociologist 
presents the population of a city or country for successive years by using 
years as the marks of classes, — laying these off along the ,r-axis, — and 
the population for the.se years as ordinates. 

Negative values easily represented graphically. We often desire to plot 
negative values as well as positive values, and this is easily accomplished 
by a slight extension of what has already been done in connection with 
Fig. I. With the data exhibited in Fig. i it might have been found con- 
venient to use the mean as the origin and to plot the frequency with respect 
to deviations from the mean. Since the mean is in this case 7.25, we have 
the following set of deviations and corresponding frequencies to plot : 





Deviations 


-3-25 


-2-75 


-2.25 


-"•75 


-1-25 


-0.75 


-0.25 


0.25 


0.75 


1-25 


1-75 


2.25 


2-75 


Frequencies 


I 


I 


8 


33 


70 


1 10 


.76 


172 


124 


61 


32 


10 


2 





We should now lay off the positive deviations toward the right from the 
origin O (Fig. 2) and the negative deviations toward the left from O. The 
frequencies should, of course, be plotted upward from X'X, just as in Fig. i. 
The result of plotting this frequency distribution is shown in Fig. 2. This 
should bring home to the reader, who is not very familiar with the use of 
negative numbers, the fact that negative numbers may be just as " real " 
and useful as positive numbers. 

The frequency polygon of Fig. 2 does not differ in form from that of 
Fig. I. It is only differently related to the lines of reference (9 A' and OV. 

Graphical meaning of median, mean, and mode. If in Fig. i we select on 
the curve a point whose ordinate divides the area under the curve into two 
equal parts, the absci.ssa of this point is the median of the population. The 



APPENDIX 



689 



abscissa of the center of gravity of the total area under the curve is the 
Jiieaii of the population, and the abscissa of the highest point on the fre- 
quency curve is the theoretical mode of the population. 




) -1.25 -0.7o-0.26 0.25 U.I 

Fig. 2 

Graph of a mathematical function. A numberj' is said to be a mathematical 
function of a number .1- if to assigned values of x there correspond definite 
values of J'. 

Thus, if_y = ix,y is a function of .r, 
since for any assigned value of .r we 
can compute^'. In general, if .r and j' 
are connected by an equation each is a 
function of the other. The study of 
certain functions is of the first rate in 
importance in the mathematical theory 
of statistics, and this is much facili- 
tated by the use of the graph of the ^" 
function in question. We therefore 
proceed to show how to form the graph 
of a few simple functions so as to 
give the general notion of the graph 
of functions. 

Take coordinate axes, as in Fig. 3, 
which divide the plane into four quad- 
rants. If the abscissas are positive, pj^ , 
they should be laid off to the right 

of 0\ if negative, they should be laid off to the left of O. The ordinates, if 
positive, are to be laid off upward from the .r-axis ; if negative, they are to be 
laid off downward. Then whatever two numbers (positive or negative) are 
given as abscissa and ordinate, the corresponding point can be located. 




A' 



690 



APPENDIX 



Let us take as an illustration the plotting of the graph of j' = ix + 4. 
Here we see from the equation that corresponding to any value assigned 
to X we get a value of v equal to twice x plus 4. The corresponding values 
are as follows : 





X 





I 


2 


3 


4 


5 


— I 


—2 


-3 


-4 


-5 


y 


4 


6 


8 


10 


12 


M 


+ 2 





—2 


-4 


-6 





Locating, in Fig. 3, the points corresponding to these values, and draw- 
ing a smooth curve through them, we have the graph of the function. This 
graph is a straight line. 

We leave as an exercise for the student to find the graph of j = x^. For 
application of graph of function, see "Probability Curve," Section VL 



SECTION IV — "SMOOTHING" OF FIGURES 

Sometimes the frequency distribution of a population arranged with 
respect to some character has many small irregularities which arise merely 
from the way in which the measurements were taken and grouped. In 
such a case a process called " smoothing " can often be employed to 
obtain regularity. A noteworthy instance of smoothing is to be seen in the 
adjusting of the population census with respect to age, there being a great 
many more people who report their ages as 40 than as 39 or 41. In 
fact, sometimes the unsmoothed figures show one half more people of 
age 40 than of age 39 or 41. It is, then, manifestly desirable to smooth 
these census returns if they are to give even an approximately correct 
impression. 

In representing such a distribution graphically we have to draw a smooth 
line in the neighborhood of the points, but not necessarily through any of 
them. This smooth line is the result of the attempt to present what the 
distribution would be if the causes of the small irregularities could be 
removed. Sometimes it is convenient to smooth figures without resorting 
to a graph. There are some rather refined but complicated algebraic 
methods ^ of doing this, but in general a very simple method can be used. 
To explain this method, take the following frequency distribution (which 
was obtained by measuring the circumferences of 995 ears of corn), in which 
the groupings into |-inch classes are not well selected. 





Inches 


4-5 


4-75 5-0 


5-25 


5-5 


5-75 


6.0 


6.25 


6.5 6.75 


7.0 


7-25 


7-5 


7-75 


8.0 


8.2s 


8.5 


Frequencies . . 


2 


4 


13 


24 


20 


74 


125 


98 


181 


98 


20S 


55 


67 


10 


II 


3 


2 



1 Darwin, Philosophical Magazine and Journal, July, 1877. 



APPENDIX 



691 



It may be well to explain the chief source of this irregularity. This 
can be seen by observing two classes, such as the 7-inch class and the 
6.75-inch class. As the measurements were recorded to the nearest tenth 
inch, the 7-inch class includes the measurements recorded as 6.9, 7, and 
7.1, while the 6.75-inch class includes only those recorded as 6.7 and 6.8. 
This should evidently produce a biased result. Instead of making a new 
frequency table with a different grouping, we may substitute for each 
frequency a number derived by smoothing. This smoothing can be accom- 
plished by substituting for each frequency, except the two extreme ones, 
the mean of the given frequency and the one immediately before and 
the one immediately after it. Thus, for frequency of ears of length 4.75 

2 + 4 -|- I ■? 
inches we should substitute = 65. But as this is only an approxi- 
mation, we may as well take the nearest integral value, or 6. For an extreme 
frequency, we substitute the mean (to nearest integer) of the extreme fre- 
quency taken twice and the adjacent frequency taken once. Thus, for the 

2 + 2+4 
frequency corresponding to length 4.5 inches we substitute = 2f, 

or, in integral numbers, 3. It is sometimes desirable to apply this process 
more than once to a given distribution in order to give it the desired 
regularity. 

The results of the scheme for the given frequency distribution are as 
follows : 





Inches . . . . -| 


4-5 


4-75 


5.0 


5-25 


5-5 


5. 75 6.0 


6.25 


"6.5 6.75 


7.0 


7.25 


7-5 


7-75 


8.0 


8.25 


8.S 


Unsmoothed J 
frequencies | 


2 


4 


13 24 


20 


74 


125 


98 


181 


98 


208 55 


67 


10 


II 


3 


2 


ist smoothed 
frequencies 


r 

t 


3 


6 


14 


'9 


39 


73 


99 


135 


126 


162 


I 20 


uo 


44 


29 


8 


S 


2 


2d smoothed 
frequencies 


f 

t 


4 


8 


•3 


24 


43 


70 


1 
102 j 120 


141 


•38 


131 


91 


6i 


27 


14 


5 


3 





In general algebraic terms, if z\, 7'.,, •• •, 7',, are the marks of classes and 
<Zj, a.2, ■ ■ ; a„ the corresponding frequencies, in smoothing the <i's we should 
substitute for them the following values respectively : 

2 «! + a., a^ + <•;., + a^ «., + a^ + a^ (i„-i + ^«-i + ^,1 ^»-i + 2 a„ 



It can be easily seen from these algebraic expressions that the arith- 
metic mean of the measurements is scarcely affected at all by smoothing, 
but that the mode is sometimes considerably changed. In general, the 
"standard deviation" (to be discussed in Section VII) is but slightly 
affected by smoothing. 



692 APPENDIX 

SECTION V — APPLICATION OF THE THEORY OF 
PROBABILITY 

The reader should understand thorou'^dily that what is commonly known 
as a " law of nature " is a generalization based upon experience, and that such 
a law cannot be proved in the strictly logical sense, but only in the sense of 
establishing a high degree of probability in its favor. To illustrate, we may 
take one of the best-established facts of physical science, namely, that all free 
bodies are attracted by the earth. The evidence for this statement consists 
in the fact that the thousands and even millions of bodies which have been 
observed have, without exception, followed this rule. This has established 
a very high degree of probability. It is altogether conceivable, however, 
that some body exists which would be repelled by the earth. Although 
experience has established an overwhelming probability against such an 
occurrence, we must not overlook the fact that experience has proved the 
statement only in the sense that it has established a high degree of proba- 
bility. It has done this and can do nothing more than this. It is doubtful 
whether any person living hr.s seen a hundred pennies tossed at random, 
all of which came heads up, and still it is possible that this might happen. 
Even if no one has seen them fall with all heads up, we are clearly not 
justified in concluding that there will always be some heads up and some 
tails up. If a thousand pennies be tossed at random, the probability that 
they will all fall heads up is so small that we may safely say, if the whole 
human race were to devote a generation to the tossing of pennies, a thousand 
at a time, there would still be a very small probability that any one would 
toss all heads. All this goes to show that certain possible events have such 
a slight probability that we should not expect them to happen in the lifetime 
of a given individual. Just so, as time goes on and observations are made in 
greater numbers, exceptions may be found to any of the so-called "laws of 
nature." Such exceptions are, however, in many cases exceedingly unlikely. 

It is hoped that the foregoing paves the way for the statement that, 
while in this subject many results may be stated in terms of probabilities, 
these results do not differ in reliability on that account from those of any 
other science based on experience. If a thousand pennies be tossed at 
random, there is nothing more uncertain than that a given penny will 
be heads, but it is a matter of common experience that the ratio of the 
number of heads to the total number of pennies tossed is, in general, nearly 
one half. We may here recall the statement of Section I, that the theory 
of probability is needed in this subject because we deal with occurrences 
and characters of such a nature that we wish to make statements in regard 
to a large number of them taken together. It is a matter of common experi- 
ence that results, such as averages and ratios obtained from large numbers 
of cases, are nearly stationary. We find the average stature of a thousand 
individuals selected at random from a large population, and are much sur- 
prised if, upon taking another random sample of a thousand from the same 



APPENDIX 693 

population, their average stature differs materially from that already found. 
We are not at all surprised if the averages are substantially equal. There 
are, no doubt, many causes which influence the growth of each individual 
differently, but when they are all taken together these small disturbances 
tend to counterbalance each other. In short, it is regularity in large num- 
bers which we expect. While it may be common sense to expect this, we 
shall later give a mathematical measure known as the " probable error " to 
indicate what deviations we should expect in results such as averages derived 
from a random sample. This discussion leads us to the following definition 
of probability. 

Definition. If\ in tJic lo/ij^ n//i, oitt of n possible cases in eacJi of ivliicJi 
an event occurs or fails to occur, it occurs n times and fails to occur n — //^ 
times, tJie probability that the event occurs on a given occasion in question 

is - \ and the pixibabilitv that it fails to occur on a iri7'cn occasion is ^ • 

n -^ '^ // 

In framing this definition we idealize our actual experience. We say 
the probability of a penny's turning up heads is one half. This may be 
looked upon as an answer to the following question: What proportion of 
the pennies tossed should we expect to find with heads turned up if we 
should continue tossing indefinitely.'' 

This idealization, for purposes of definition, is analogous to the idealiza- 
tion of the crude chalk mark into the straight line of geometry. Since the 

sum of the probabiHties of occurrence and failure is — -\ ^ = i, the 

;/ // 

number i is the symbol of certainty. The expression " relative frequency " 

conveys fairly well the idea of probability. 

The following corollary is often easier to apply than the definition. 

Corollary. If t/ie entire tiumber of possible cases in which an e7ient is in 
question can be analyzed into n' cases, each of which is equally likely, and 

m' 
///' is the number of these cases in wJiich the event occurs, then — 7 is the 

n 
probability of the event. 

Thus, in tossing two pennies, what is the probability that one will be 
heads and one tails } 

There are four different ways in which the pennies may fall : Head and 
tail, tail and head, head and head, tail and tail. Two of these ways lead 
to the occurrence of the event. Hence | = \ is the desired probability of 
one head and one tail. 

Combination of probabilities. TJic probability that all of a set of independ- 
ent e7'ents will occur on anv occasion in which all of them are in question is 
the product of the probabilities of the single events. 

Proof. Let p-^, p.^, ■■■,p^he the separate probabilities of ;- events. Out 
of a great number, //, of cases, the first will happen on p^n occasions. Out 
of these the second will happen on p.^ (pin) occasions. Continuing this 
process, and applying the definition of probability, the theorem is at once 
established. To illustrate, suppose that among a population of a hundred 



694 APPENDIX" 

thousand people thirty thousand are vaccinated, and that five hundred per- 
sons have smallpox. If vaccination has no intiuence on the number of cases 
of smallpox, what is the probability that a person will be both vaccinated 
and have smallpox ? 

Since one hundred thousand is a large number, we may give 



30000 3 



I 00000 10 



= probability that a person is vaccinated ; 



500 I 

= = probability that a person has smallpox ; 



1 00000 200 

10 200 2000 

and has smallpox 



probability that a person is both vaccinated 



3 

Furthermore, x 1 00000 = i i;o, the number of persons we should ex- 

2000 

pect both to be vaccinated and to have smallpox, if vaccination has no 
influence on the number of cases of smallpox. 

Illustrations of probability. Let us ihroiv out upon a table at raiidoi/i four 
pennies ; what is the probability that exactly r of them luill be heads and the 
rest tails when r takes values o, /, 2, j, ^ ? 

(i) Probability that o will be head and 4 tails is (i)* 

(2) Probability that 1 will be head and 3 tails is 4(5)* 

(3) Probability that 2 will be heads and 2 tails is 6(i)^ 

(4) Probability that 3 will be heads and i tail is 4(3)* 

(5) Probability that 4 will be heads and o tail is ({j)^ 

In (2) the coefficient 4 appears before (J)^ because with four coins there 
are four different combinations^ possible, each consisting of 1 head and 3 
tails. Similarly in (3) the coefficient 6 appears because with four coins 
there are possible six combinations, each consisting of 2 heads and 2 tails. 

The above illustration may be generalized and the result put into the 
following form : 

If « coins are thrown upon a table at random, the probability that exactly 
r of them will be heads and the rest tails is given by the r+ 1st term of 

/I I \ " 
the binomial expansion ( + :; ) ; that is, in other symbols, "C,.{f)", where 

the symbol "C^ indicates the number of combinations of n things taken r 
at a time. 

In order that the reader may more fully appreciate the greater prob- 
ability of getting an almost equal number of heads and tails in tossing 
pennies than of getting widely different numbers, we present the following 
table for n — 999, obtained from Quetelet's Sur la thdorie des probabilites. 

1 For definition of a combination, see te.\t, p. 511. 



APPENDIX 



695 



Columns i and 2 give the number of heads and tails whose probability 
is in question. Column 3 gives the probability of exactly the number of 
heads and tails indicated in columns i and 2. 





I 


2 


3 


I 


2 


3 


Heaus 


Tails 


Probability 


Heads 


Tails 


Probability 


499 


500 


930C-500(Jr'= 0-025225 


450 


549 


0.000 1 863 


490 


509 


^^C500(l)^^= 0.021069 


440 


559 


0.0000209 


480 


519 


^^^C5i!,(lp»=o.oii794 


430 


569 


0.0000016 


470 


529 


9^C529(.ir9= 0.004423 


420 


579 


0.00000004 


460 


539 


^^^^539(^^^=0.001 I 10 









A glance at the table shows that, in the long run, one should expect 499 
heads and 500 tails more than 600,000 times as often as 420 heads and 579 
tails. In this connection it is interesting to inquire into a case mentioned 
on page 692, namely, the probability of getting all heads in a single throw 
of a thousand pennies. This probability is 



(j\ 1000 
2/ 



(an integer containing 302 figures) 



and the statement made on page 692 as to the human race (population 

1,500,000,000) devoting itself to tossing pennies is clearly a safe statement. 

The results in the above table may well be exhibited graphically (Fig. 4). 




4,tO 
549 


460 
539 


470 
529 


4<S0 490 499 500 509 519 
519 509 500 499 490 480 

Fig. 4 

Scale: Vertical, i inch=o.oi 
Horizontal, i inch= lo 


529 

4ro 


539 

4G0 



696 



APPENDIX 



If we had taken all the intermediate integers from 499 with 500 to 440 
with 559, we should have had ten times as many points which would 
arrange themselves along the curve in Fig. 4. By increasing the number 
of coins and decreasing the horizontal scale, we can get the points as 
close together as we please. This curve in Fig. 4 is the so-called prob- 
ability curve and it approaches very nearly the curve of error, or normal 
frequency curve, which we are now prepared to discuss. 



SECTION VI— NORMAL PROBABILITY CURVE 

It has been found that the frequency curves of a great many biological 
measurements follow a curve variously known as the " probability curve," 
" normal probability curve," " curve of error," or " normal frequency 
curve." In particular it is known as the "curve of error," because if 
errors which an observer makes in a refined set of direct measurements 
on a given quantity be plotted as abscissas, the corresponding ordinates 
of points on this curve represent the frequencies or probabilities of the 
errors. 

Y 




The general form of the curve is shown in Fig. 5. The origin is taken 
at the mean. Then, if any mark of a class is above the mean, its devia- 
tion is positive, and it would be plotted to the right from the origin O, while 
if the mark of a class is less than the mean, its deviation is negative, and 
it would be plotted to the left from O. For the benefit of those who are 



APPENDIX 697 

familiar with the calcukis, the derivation of this curve will be treated in 
a footnote/ but a complete understanding of this footnote is not necessary 
for reading what follows. 

While the equation of this curve has been derived in many different 
ways by arguments based on a few assumptions as to the nature and causes 
of deviations from the mean, it must be granted that these assumptions are 
of such a nature that experiment is an important test as to whether a 
frequency distribution is of this type. The reader should be on his guard 
against the mistake that deviations from the mean, in all classes of measure- 
ments, follow closely this law of frequency. "-^ In fact, Pear.son has found 
that in many cases frequency distributions obtained in biological study can- 
not be so well titted by the normal curve as by what he calls generalized 
probability curves, which take " skewness " and limit of range into account. 
These curves lead us into mathematical complications which cannot be well 
treated here, but it may be remarked that he obtains these curves from the 
point binomial {p + ^)", where/ + ^ = i, but/ -^ q, and from a hypergeo- 
metric series. 

1 While Gauss, Laplace, Qiietelet, Heischel, and other great mathematicians have derived 
the equation of the normal curve, and all agree in the result, they differ widely as to hypoth- 
eses upon which they base the derivations. 

We present here a derivation based upon tlie hypothesis (see Pearson, Philosop/iical 
Tratisadions, CLXXXVI, A, pp. 343-381) that the normal curve represents a function 
y = <f>{x) which has a certain slope condition obtained from the point binomial polygon 
(i + i) "^ (S2^ P'§- 4)- This slope condition may be stated as follows : 

slope of side _ 2 mean abscissa of side 



mean ordinate of side 



the v-axis being the axis of symmetry and the cr being the same for all sides. 
In calculus form, this condition would be 

y dx 2 (t2 

Integrating, ;■ — ke ^''''■• 

The constant k can be determined by finding the total area under the curve and equating 
this to the total population n which the area represents. This gives 



c VaTr' 
and the final form of the equation of the normal curve is 

y=^^e''^' (I) 

a V2 TT 

in which (J will later be shown to be what we shall call the "standard deviation" and 
£ = 2.718 • • •, the base of Napierian logaritlims. 

If equation (i) is to give probabilities instead of frequencies, we must replace 11 by i in 
equation (i). 

2 For fulfillment of the normal law in nature, see Edgeworth, Stathtualjciirual, Jubilee 
Number, 18S5, p. iSS. 



698 APPENDIX 

However, the normal curves give, in general, at least a valuable first 
approximation, and we shall follow the usual method of employing statis- 
tical constants derived from this curve ; for these constants are significant, 
even if the distribution is not normal.^ 

Area under the probability curve has an important meaning. If we select 
unit area as explained in Section III, the area represents the total population, 
and the area between the two ordinates, the curve, and .t--axis represents the 
number of variates between these ordinates. If we look upon the curve as 
representing probabilities instead of frequencies our horizontal scale is 
unchanged but our vertical scale must be multiplied by the total popula- 
tion. Thus, if the population is 800, as in the case of Fig. i, we should say 
that what there represented unity should be multiplied by 800 in order that 
it shall represent unit of probability. Then the entire area under the curve 
will be unity, and the area between two ordinates, the curve, and jr-axis is 
simply the probability that a variate selected at random would lie within 
this interval. 

SECTION VII — PROBABLE ERROR AND STANDARD 
DEVIATION 

If we have estimated the population of a city at 100,000 and have 
good reason to think that the chances are even that this is correct within 
1000, we give much more information by stating that the population is 
100,000 ± 1000 than by giving merely the figures 100,000 and leaving the 
reader entirely in doubt as to the accuracy of the determination. 

In describing a frequency distribution the average gives absolutely no 
idea as to whether deviations are large or small, — nothing in regard to the 
spread of the distribution. It is the object of the "standard deviation " to 
be descriptive of this variability, and it is the object of the so-called 
"probable error" to indicate what confidence is to be placed in statistical 
results. The use which has been made of both "standard deviation" and 
" probable error" makes it unnecessary to dwell longer on this point, but 
it is our purpose here to show how the formulas used in the text are derived. 

Probable error of a single variate. T/w probable error of a single variate 
of a population is dcfned as that departure from the mean., on eitlier side, 
within which exactly one half the variates are found. 

By the use of the probability curve (Fig. 6) the probable error may 
easily be explained geometrically when we look upon the entire area under 
the curve as representing the total population. In Fig. 6 we draw two 
ordinates, 6'7"and S'T', equally distant from the mean, and such that one 
half of the entire area under the curve lies between them, in other words, 
is bounded by the curve, the .r-axis, ST, and S'T'. Then ± 06" represents the 
probable error of a single variate. If we .should use a single variate selected 
at random to represent the population it is an even chance that that single 
variate would be less or more than (96' from the best value. 

1 See Yule, Proceedings of the Royal Society, LX, 477-4S9. 



APPENDIX 



699 



An approximate value for the probable error of a single variate in any 
population may be easily obtained in the following manner : 

1. Arrange the variates in the order of magnitude. 

2. Count one fourth of the variates of least measurements and note the 
measurement of the upper one of these variates. Let u represent this 
measurement. 

3. Count one fourth of the variates of greatest measurements and note 
the measurement of the lower of these variates. Let v represent this 
measurement. 

7' — // 

4. Then gives the probable error of a single variate. 

The formula for the probable error in a single variate is 
Es — 0.6745 



where 2-r- means the sum of the squares of the deviations from the mean 
and // is the number of variates. The conception of the probable error of 

r 




X 



a single variate is of value because it aids in the derivation of the probable 
error of other important results. The formula for the standard deviation 

is (page 429) -1 /^^ , so that the probable error of a single variate is obtained 

from the standard deviation of the population by multiplying the standard 
deviation by 0.6745. 



700 APPENDIX 

As has been pointed out in the text, the standard deviation gives a good 
idea of the spread of the distribution. From the accompanying footnote ^ 
we are naw in a position to appreciate its mathematical significance. It 

is the (T in the equation y = 7=^ "' of the normal probability curve, 

and bears a similar relation to the probability curve that the radius of a 
circle bears to the circle. If o- is small the probability curve is crowded 
together so as to resemble curve A in Fig. 7, while if a is large it is spread 
out so as to resemble curve B in Fig. 7. 

Hence the standard deviation along with the mean completely describes 






the distribution when it is normal." The expression \/^^— , which is thus a 

>» // 

perfect measure of variability for a normal distribution, is a good measure 

of variability when the distribution is not normal, but it is not completely 

descriptive of the population. 

Another measure of variability is sometimes used which consists simply 

in taking the arithmetical average of the /i deviations, — these deviations 

being given the positive sign. 

1 This may be written more briefly as 

■S.X2 

P= ' -/ ^"^{l^x)". 

c" (2 7r)2 

For a given set of deviations which occur, cr should be selected so as to make tha 
probability P a maximum. ,„ 

Equating the first derivative — - to zero, \ve obtain 

■S 1 2 "S yZ 

^= — "— r^ .-i 2;;c3 - -^ -"- /"?^^= o, 
dv , " (Ti , '1 (r''-n 

or 2a:^ — ncr- = o. 

n 
Now, by means of integral calculus, tables are formed of the area included by the curve 



(7"V27r 



2 0-2 



the .JK-axis, and any two ordinates at equal distances i a from the mean. .Such a table with 
the argument - is found in Davenport's Statistical Methods, second edition, pp. 119-125. 
This table shows that 

X 

-=0.6745 (0 

when just one half of the area under the curve is included as described above. By definition, 
the particular value of .v given by (i) is called the probable error in a single variate, and we 
shall represent it by P-s. 

Hence, £s = .6745 <T. 

- See Gallon, Natural Inheritance, p. 62. 



APPENDIX 

The formula for this is simply 

|.rj + l.r., I + ■•• + l-v,, 



701 



where the marks | | indicate that the numbers should all be taken with the 
positive sign. 

This measure of variability is usually known as the ai'erage dcination. 

As to the relative merits of these two measures of variability, the stand- 
ard deviation is to be preferred. Its relation to the probability curve as 
indicated above gives it special favor mathematically, although a geometric 
meaning may also be given to the average deviation. 

Probable error of the mean. Since in natural science results are, in gen- 
eral, based on averages, we are more directly interested in the probable 
error in the mean than in the probable error of a single variate, although 




the latter conception is desirable as a basis for understanding the former. 
We can best discuss the probable error in the mean by beginning with an 
illustration. 

Suppose that, in determining the average stature of a male population 
consisting of a million individuals, we select at random groups of a thou- 
sand each. We could then, in all, have available a thousand such groups 
using no individual twice. It is an axiom of statistics, as we have already 
explained, that the mean statures obtained from each of these groups will 



702 APPENDIX 

differ but slightly from each other, but if the measurements are sufficiently 
accurate there will be some differences. If we should find the inciDi of 
these means (we may call it the second mean) we could plot a frequency 
curve of the distribution of means just as we have for the deviations 
of the original variates. Of course this curve would be much crowded 
together, like A of Fig. 7. To make this general, with a very large popu- 
lation, and with n in each group instead of 1000, the following result is 
obtained : 

If £"5 is the probable error of a single variate, that of the mean of n 
variates is 

that is, to find the probable error of the mean, divide the probable error 
of a single variate by the square root of tJie munber of variates. 

Probable error in standard deviation. Taking up again the million cases 
of stature divided into a thousand groups as an illustration, supposing that 
the standard deviation of each of these thousand groups be found, we 
should see that they differ but slightly. However, if the computations and 
measurements be very refined there will be deviations. These standard 
deviations constitute a frequency distribution whose standard deviation 
can be found, and the probable error of the standard deviation can be 
obtained just as we have shown in the case of a single variate. 

Generahzing this so as to have a very large number of groups each con- 
taining n variates taken as a sample to represent the population, the prob- 
able error of the standard deviation is 

that is, to find the probable error in the standard deviation, dii'ide the 
probable error in the mean by V2. 

Formulas for probable error in some important statistical constants. Enough 
has now been said to give the conception of the probable error in any 
statistical determination and a general notion of the methods by which 
formulas for the probable error are derived. 

It is scarcely necessary to remark that the probable error does not take 
into account evident mistakes either of observation or computation. We 
are assuming that these have been eliminated. It has to do with errors 
(deviations) due to an indefinitely large number of unassignable causes 
such that the errors are distributed according to the laws of probability. 

It seems unnece.s.sary to continue the discussion of probable error in 
other determinations, but it does .seem well to collect together, for purposes 
of reference, the formulas for the probable error in some of the most 
important statistical constants. 



APPENDIX 703 

In what follows 

o" is to represent the standard deviation ; 
;/ is to represent the number of variates ; 
c is to represent the coefficient of variability ; 
;- is to represent the coefficient of correlation. 

1. E, = 0.6745 ^ = probable error in a single observation. 

E, 0.6745 o- , , , . , 

2. E^i = —^ = 7= — = probable error in the mean. 

Vy/ V// 

E ,r 0.6745 O" , , , . 1 1 1 • • 

-i. E = —i= = = — = probable error ni standard deviation. 

^ " V2 V2;/ 

0.6745 f 

4- ^c = , — 
V 2 ;/ 



I + 21 I ' = probable error in coefficient of varia- 

V°°/ -I bility 



0.6745 C .,.,,. 

= approximately, if L is not greater than 10 per cent. 

•V2« 

5. E^ = — — — j= = probable error in coefficient of correlation. 



0.67450-, jl— /'2 , ,, . , . en ■ ^ 

6. E^ = yj = probable error in the regression coefficient 



r 



SECTION VIII— CORRELATION THEORY 

Definition. T7i'0 iiicasiirable cJiaracters of an individual, or of related 
individuals, are said to be correlated if to a selected series of sizes of the one 
there correspond sizes of the other whose mean values are functions of the 
selected values. The word "sizes," here used, should be taken to mean 
" numerical measure." 

For the sake of concreteness and simplicity, we may think of measuring 
the correlation of sons with respect to their fathers. To render the above 
definition in symbolic language and to develop the method of determining 
the function mentioned in the definition are the first points in the application 
of mathematics to the theory of correlation. For this purpose, let x and/ 
represent variables such that j = <^(.r) gives the mean value oiy correspond- 
ing to a selected x. Then the problem is to determine <^(.i). 

Suppose the following system of corresponding values results from 
measurement: {x\ y'), {x",y'), ■■■, (.i-<"\ y'-"^), where u is a very large 
number indicating the population of fathers and corresponding sons. 
The.se observations are said to form a total population or universe of 
observations. As it will be more convenient to deal with the deviations 
of the observations from their mean value than with the measurements 
themselves, let (-Vi.Ji), (-v.„/.^), •■ ■, (-r,„y„) represent the deviations of 



704 



APPENDIX 



the ol)servatinns from their nieun value. These deviations may be con- 
veniently represented with respect to coordinate axes (Fig. 8). 

By the range along the .i-axis we shall mean such an interval that ordi- 
nates drawn at the extremities of the interval include between them the 
total population. Thus, in Fig. 8, the range is taken from a to b. This 
range may well be divided into some number, say s, of equal parts, each 
of width A.r, by ordinates at the points of division. If we let x(, .I'/i • • -i 
.r/ be the abscissas of the feet of the ordinates through the middle points 
of the j- cla.sses, we shall call these the marks of the classes of j's. The 
values of J which belong to a given class of x are said to form a j-array. 



A'^ 




Let the crosses (x) in Fig. 8 represent the means of the j/'s in each of 
the ^--arrays. If correlation exists, these means do not lie at random over 
the field, but arrange themselves more or less in the form of a smooth 
curve called the " curve of regression." This curve is a crude picture of the 
function which defines the correlation of the j-character relative to the 
.r-character. Experience has shown that, in many sets of measurements, 
this line is approximately a straight line. For this reason, and for sim- 
plicity, the line subjected to the condition that the sum of the squares of the 
deviations (measured parallel to the j-axis and weighted with number of 
points in array) of the means from it shall be a minimum, is called the 
"line of regression." When the means lie exactly on the line the regres- 
sion is said to be " truly linear." 



APPENDIX 



705 



The algebraic details of subjectin.ii; a line to this minimal condition are 
well known to those familiar wilii the method of least scjuares. The ecjua- 
tjoii of the resulting line is 

(T,,.V 

/ = '■-, (0 

where o-^. is the standard deviation of the population with respect to the 
.i--character, o-,, is the standard deviation with respect to the j'-character, 
and r is the correlation coefficient given bj' 

''= , 

where the summation is extended to every two corresponding variates of 
the population. 

Similarly, the regression of the .1 -character with respect to the j'-charac- 
ter is given by 

x = r—v. (2) 

It should be noted that (2) cannot be obtained from (i) by solving for 
.V in equation ( 1 ). 

Standard deviation of arrays. Suppo.se that the regression is truly linear, 

o-,, X 

so that the means of the j'-arrays fall on the line j' = r^ — , and furthermore 

that the standard deviations of all parallel arrays are equal. Then the 
standard deviation of any array must be given by 

// 
where the summation extends to the entire population. 
rrr, X 



' 2j'" 2 0-,, ;'2.iT ra-^r'SiX^ 



n n cr, // 

= (r,-(l -r-^). (3) 

Hence the standard deviation of aj/-array is obtained from the stand- 
ard deviation cr,, of t he tot al population with respect to the _y-character by 
multiplying o> by Vi — r-. 

Since the first number of (3) is a sum of squares divided by //, the 
s_'cond number must be positive. Hence 

-!<;-< I. 

This shows that our correlation coefficient must take values between + i 
and — 1 . 



7o6 APPENDIX 

li r = + I, all the individual points of the population will lie on the line 
of regression, and we can therefore, when one character is given, tell 
exactly what the associated character is in magnitude. In this case the 
correlation is said to be perfect positive correlation. Similarly, if r = — i, 
the correlation would be perfect negative correlation. 

Three variables. The theory of correlation is easily extended to apply to 
more than two variables. For example, we might investigate the correlation 
of the statures of sons with respect to the statures of both parents. This is 
the case of biparental inheritance treated in the text, page 529, and the for- 
mulas there used must be special cases of those which we are about to derive 
for giving the most probable value of a variable s where s is the numerical 
value of a character correlated with characters of measurements a' and^. 

Suppose that the following system of corresponding deviations from the 
means have resulted from measurement: (-I'l, Jii.s'i), ('t'2'.^2' ^2)' i^'s^fa^ •^3)' 
• • • ) 0',nj>n^,t)- Represent these measurements with respect to coordinate 
axes in three dimensions. These axes are to be taken at right angles to 
each other, as is conventional in analytic geometry, and may be referred 
to as the x,j, and s axes. It now requires two letters to mark an array of 
^'s. We shall call (-^Vj j/) the mark of a class. Now imagine the means 
plotted for every .s^-array. If correlation exists, these means will not lie at 
random in space, but will arrange themselves approximately on a surface 
called the " surface of regression." The equation of a surface is of the form 
2'=y(,r, _y). We shall consider only the case where thisy-function is of 
the first degree, for the same reasons that we considered only the case of 
a first degree function in the case of correlation of two variables. 

It results that the required function is 

f — )' y Cf V — T V (T 

' xz ' XV yz ^z , ' yz ' xz' xy^z x x 



where r^,. is the correlation coefficient between the /-and ^--characters, and 
similar meanings are to be given to the other r's, as indicated by the sub- 
scripts. This equation gives the mean value of the ^-arrays corresponding to 
given X and/, if they can be given by a linear function. If they cannot be 
accurately given by a linear function, this equation must merely be looked 
upon as giving a first approximation. 

Standard deviation of arrays. If the equation (i ) be used to estimate the 
value of the s-character corresponding to a selected x and j, we have the 
square of standard deviation of each s-array about this estimated value 
given by the expression 

S {2^ -ax- byy 

n ^ ^ 

as an average value, where the summation extends to all the observations ; 
and 

a = ^-ir- — ) and b — — ^ — . 

I - ;\„- a,, I - ?- - o-^ 



APPENDIX 707 

When expanded and expressed in terms of ;-'s and o-'s, (2) becomes 

I ' p-V ^ '•*-»-' 1-1' '?-l' '. 

(3) 

The formulas used in the text in discussing biparental inheritance are 
special cases of (i) and (3) just derived. This may be verified by making 
the following substitutions : 

Put x = //p J' = /i.,, r = //.,, ;-,,, = ;-„, ;-,_ = rj, r^.^ = r^, cr. = o-g, a^ = ctj, 
o-,, = cr., . 

Then in the new notation (i) becomes 

K = - — V — /'i + ~ — V — K ■ (4) 

Since in the case discussed in the text the parents were taken ecjui- 
potent, f\ = /:,, and by making this substitution in (4) we get 

' ( ' + ''3)0-1 V 0-2 

which is the formula used in text. Likewise, if we make these substitutions 
in (3), we get for the variability of an array of sons 



°"3\/ 



I +f\ 



which is the formula used in the text. 

More than three variables. It is easily seen that the methods employed 
in the case of two and three variables can be extended to any number of 
variables. However, the complexity of the algebraic expressions becomes so 
great that it does not seem well to present a more extended discussion here. 
For the general case of any number of variables, the reader with consider- 
able mathematical training is referred to the treatment by Karl Pearson in 
the Philosophical Transactiotts of the Royal Society, A, CLXXXVII, 1896, 
and A, CC, 1903. In the papers just referred to the general expression is 
also given for the variability of an array in the case of any number of 
variables. It is from this general expression that the formula used in the 
text for the variability of an array of offspring after n generations of 
selection is derived. 

Formula for the correlation coefficient r which is better adapted to numer- 
ical calculation. In the first place, the calculation of the standard devia- 
tions of both systems of variates should be done by the shorter method 
presented on page 465. 



7o8 APPENDIX 

The value; obtained for ;■ on page 705 is 



where x andj/ represent deviations from the means, and the summation is 
extended to every pair of corresponding deviations. The calculation of 

can be much shortened by an equivalent formula which we shall 

n(T ^ o-,, 

now derive. Following the notation on pages , let G ^^ and C,. 

represent class marks near the means of the systems of variates indicated 
by the subscripts, and C^, (7,, corrections to these class marks which give 
the correct mean values so that 

M., = G, + C, , 
My = Gy + C,, . 
Let x" 1 y' represent deviations from G ^. and Gy which correspond to 
deviations x^y from the mean. Then 
.1- = x' - C, , 

^{^■' - C^,){y' - Cy) 
r = , 

_ ^x'y' - C;^x' - C^-^y' + 2C,.C, 

_ ^x'y'- Cy^jx + C) - C2(j + C,,) -f 2C,C_^ 

^ 2:ry - sec, 

Xv'y' \ I 



This is a formula much better adapted to computation than the formula 
_ 2-iJ 
//cr.o-,, ' 
Its application is shown in the text, page 465. 

SECTION IX — RANDOM SAMPLES 

We know full well that we cannot, in general, measure all the individ- 
uals of a race or population whose characteristics we wish to describe. We 
are obliged to get our information and to construct our science by the 
selection and examination of samples taken at random from a large group 
of individuals. To illustrate, it is not practicable to measure the stature 
nor, in general, any other character of all the adults in the United States. 
We must be content to deal with a reasonably small number that will make 
the measurements a feasible undertaking. 

An investigator is always concerned about the number of variates which 
must be measured in order that confidence may be placed in his results. 



APPENDIX 



709 



For instance, he asks, Of how many ears of corn taken at random must 
I measure the length in order to obtain, to a certain desired degree of 
accuracy, the varial^ility of the corn from which selection is made? Must 
I measure fifty, a hundred, or a thousand ears ? Again, how many variates 
must I take to give a reliable determination of the mean ? 

Similarly, in any correlation study he will be concerned with the num- 
ber of variates he must take in order to present a trustworthy determina- 
tion of the correlation coefficients. 

While these questions cannot be answered in advance for all kinds of 
populations, it is the object of this section to give some assistance to the 
inquiring investigator in forming a judgment in this matter. The best 
measure thus far devised upon which to base a judgment is the so-called 
"probable error." 

So far as the mean is concerned, it has been seen that the probable 
error of a single variate may be obtained approximately by counting, and 
that the probable error in the mean is obtained from that of a single vari- 
ate by dividing by the square root of the number of variates. This process 
can often be applied in a rough way before much labor has been put on a 
problem, and it becomes a useful guide where the mean alone is in question. 
It should be remembered that the probable error in any result is, in gen- 
eral, inversely proportional to the number of observations. 

A method similar to that just explained for the mean can be used to 
find the approximate value of the probable error of the standard deviation, 
since the probable error of the standard deviation is obtained from that of 
the mean by dividing by v 2. 

As for the coefficients of variability and correlation, the following tables 
show the probable errors corresponding to values of the coefficient of varia- 
bility from I per cent to 25 per cent, with numbers of variates from 25 to 
1000, and the probable errors of the correlation coefficient for values from 
o to I, with numbers of variates from 25 to 1000. 

If, then, we have an approximate notion as to the value of one of these 
coefficients, we can find from the table the probable error corresponding 
to a certain number of variates. 

To illustrate the use of these tables, suppose that we know in advance 
that the coefficient of variability is in the neighborhood of 20 per cent ; 
then with a hundred variates we see from the tables that the probable error 
would be approximately i per cent, while with five hundred variates it would 
be only 0.44 per cent. We thus decide upon the number of variates by the 
magnitude of the probable error and the degree of accuracy desired in our 
results. 

Probable error in estimate of probability from a limited number of obser- 
vations. While it has been said that, in a general way, the accuracy of a 
statistical result increases as the square root of the number of observations, 
this rule is often difficult to apply, and is an inadequate test in many 
important cases. 



7IO 



APPENDIX 






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APPENDIX 



711 





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712 APPENDIX 

A common and important class of statistical deductions, which should 
receive very critical examination, may be illustrated as follows : 

Suppose that, out of a total of ten years which have been observed, the 
apple crop in this locality has been injured by frost four years, and has 
been uninjured six years. If this data for ten years is all the evidence we 
have bearing on the probability of an apple crop, the best estimate we can 
give for the probability that the apple crop in this locality will not be 
injured by frosts in a given year is j%. If, however, our data extend over 
twenty-five years, in fifteen of which the apple crop has been uninjured by 
frost, we again give j% (if = i%) as the best estimate for the probability 
that the apple crop in this locality will not be injured by frosts in a given 
year ; and certainly more confidence can be placed in the result than when 
only ten years were taken. 

We might carry our illustration back a hundred years in sixty of which 
the apple crop in this locality has been uninjured by frosts and we should 
still give y*'^ as the most probable value of the probability that an apple 
crop in this locality will not be injured by frost in a given year. It should 
be noted that we are here dealing with the probability of a probability^ or 
what De Morgan has called the "presumption of a probability." 

The critical examination of such probabilities as the above derived 
from observation should include some criterion which will indicate the 
accuracy of the approximation when only a limited number of cases can be 
examined. Such a criterion may be found in the probable error of the 
probability. 

The problem in hand may well l)e stated in the following general form : 

A bag contains an indefinitely large number of white and black balls in 

unknown ratio ; if /// + // l^alls have been drawn as a random sample, and 

;// are white and // are black, we give as the best value of the probability 

/// 

of drawing a white ball . What is the probable error in this result.'' 

^ III + // ^ 

Or, in other words, in /// + // trials, an event has happened /// times and 

/// . 

failed to happen // times ; if we deduce from this that ; — is the probability 

m + n 

that the event will happen on a given occasion, what is the probable error 

in this result ? 

From the works of Laplace, Poisson, and De Morgan, it follo ws tha t 

, , , . >'i . . , , r , 0-6745 / W« 

the probable error in is given by the formula ± \ 

w + // ^ ■' III + n \ III + n 

Applied to our illustration of the apple crop when the data covered only 

0.6745 1-4 
ten years, this probable error formula gives + \ — = dr 0.104. 

From the magnitude of this probable error, it is at once seen that the 
result /o (derived from ten observations) for the probability that an apple 
crop will be uninjured by frost can at most be said to be but a crude and 



APPENDIX 



I^Z 



unreliable approximation. It is more than an even wager that it differs 
from the true value by as much as y'j. 

0.6745 /2400 

[GO 



When a hundred years are used, the probable error is 



\ K 



= 0.033, which shows that the result /'„ derived from a hundred years is 
much more significant than that which was obtained when only ten years 
were used. 

The following table will show how, with increasing numbers, the probable 
error in the determination of the probability decreases. 



numbek of 

Observations 

= »« + « 


NtlMBER OF 

Times Event 
HAPPENS = tit 


Probability 

}>t 

in + « 


Probable 
Error 


Numbers such that Wager is 
EVE.N that Random Sample 

AGAIN taken lies BETWEEN 

THESE Numbers 


ID 


6 


0.6 


± 0.104 


4.96 and 7.04 


25 


15 


0.6 


± 0.066 


13.35 ^"d 16.65 


50 


30 


0.6 


± 0.047 


27.65 and 32.35 


100 


60 


0.6 


± 0-033 


56.7 and 63.3 


1,000 


600 


0.6 


± 0.0104 


989.6 and 1 010.4 


10,000 


6000 


0.6 


± 0.0033 


9967 and 10033 



Remarks. In conclusion, it should probably be said that we have, in 
the foregoing brief discussion of statistical methods, touched only "the 
fringe of a great subject." We have for the sake of simplicity confined 
ourselves to the normal curve of distribution ; but it is to be hoped that 
we have given a general view, in this short space, of the methods by which 
the formulas are established which are now being commonly used in the 
quantitative study of evolution, and that the reader may come to see the 
proper place of statistical methods in solving problems of this character. 

Furthermore, it is hoped that the results as here presented will be found 
practical in the sense that they may be of use to the non-mathematical 
reader, and pave the way for further investigations along this line. 



INDEX 



Accessory chromosome, as related to 
sex, 634-637 ; Gross and Wallace 
upon, 636; Henking upon, 635; 
McClung upon, 635; Paulmier upon, 
635 ; Wilson upon, 634, 637. 

Acclimatization, bearing of, on insta- 
bility of living matter, 308-316; by 
inoculation, 382 ; effect of, upon 
transmission, 374-3S6 ; extent of, 
375' 376; in general, 105, 3 14-3' 6; 
of the individual and of the race, 374 ; 
of races, 384 ; of wood sage on high 
and low altitudes, 378 ; permanence 
of, 315; to chemicals, 308-311; to 
cold, 313; to electricity, 314; to high 
temperature, 31 1-313 ; to hot springs, 
379; to light, 313; to poisons, 381- 
382 ; to temperatures, 376, 38 1 ; trans- 
mission of, 374 ; without selection, 

379.381- 

Acid secreted by animals and plants, 
267. 

Acquired characters, 182, 30S-311 ; as 
distinct from congenital, 354-356 ; in- 
heritance of, 349 ; non-existence of, 
35S-360. 

Actinian, reaction to chemicals, 273, 
274; regeneration in the, 334. 

Adaptations, 350; not universal, 206- 
208, 412. 

Adlum, John, originator of Catawba 
grape, 134. 

Age, influence of, upon functional activ- 
ity, 94 ; influence of, upon prepotency, 

573- 
Albinism common in most species, 114. 
Amitosis, 151. 

Amoeba, response to light, 253, 254. 
Amphiaster, 147. 
Amphicyon, 50. 
Ancestral heredity, formula for, 533, 

534 ; law of, 525-534. 
Ancestral idioplasm, 173. 
Ancestral units, 173. 
Animal breeding, 654-676; advantages 

of, 654 ; disadvantages of, 654, 655 ; 

disadvantage of many characters in, 

656, 657 ; during a depression, 665, 



666 ; fashion in, 658, 659 ; by beginners, 

675; records in, 666-672; show-ring 

consequences, 660 ; testing sires and 

dams, 660-664 ; testing young females, 

661. 
Animals, growth of, influenced by heat, 

258, 259 ; higher regeneration in, 

325, 326 ; reduction in, compared 

with plants, 165. 
Ant, polymorphism of, 20. 
Antenna developed as a foot, 43. 
Apes, meristic variation in teeth of, 48, 

49. 
Apricot, mutant of the plum, 112. 
Arrays of the correlation table, 459. 
Artemia, experiments with, 283. 
Arteviia saliiia, effect on, by degree of 

salinity, 102. 
Artificial parthenogenesis, experiments 

in, 278-282. 
Assortative mating, 163. 
Aster, 147. 
Asymmetry, 70. 
Atavism, 192-194. 
Attraction of odors, 275. 
Auricular appendages in mammals, 45, 

46. 
Average deviation, 427 ; illustrated, 

441-443- 

Bacillus tuberculosis excites abnormal 

growth, 98. 
Bacteria, effect of culture medium 

upon, 229. 
Bailey, experiments in acclimatization, 

376-378 ; on bud varieties, 181 ; on 

the gooseberry, 130. 
Bardeleben, studies in mammae, 47. 
Barrenness to certain individuals, 201. 
Bathmic influences, 202-208. 
Bear, variation in digits of, 58. 
Bees, effect of food upon, 226. 
Begonia, regeneration of, 238, 331. 
Belated inheritance, 475. 
Bert, experiments in grafting, 107. 
Bioiiietrika, journal of statistical study, 

478. 
Biophors, 14, 208. 



715 



7i6 



INDEX 



Bipaieiital inheritance, 5-9-533- 

Birds, effect of heat upon development 
of, 259; variation in digits of, 56. 

Birthmarks, 189-191. 

Bisexual reproduction, a cause of varia- 
tion, 160-163; introduces no new 
characters, 163. 

Blackberry, evolution of, 131-133- 

Blemishes on breeders, 590. 

Blend in characters, 48 1. 

Blended and exclusive inheritance, 475. 

Bonnet, experiments in regeneration, 
316. 

Bonnier, experiments on acclimatiza- 
tion, 378 ; experiments with dande- 
lion, 223. 

Born, experiments in grafting, 108, 336. 

Brain not necessary to coordinated mo- 
tion, 400, 401. 

Breeder's business is the production of 
sires, 605. 

Breeders' fads, 594. 

Breeders of speed and breec'ers of 
breeders contrasted, 557. 

Breeding, polymorphism in, 476, 477; 
problems of, outlined, 3-5; purposes 
in, 599, 600 ; systems of, 599-627 ; 
true, or stability of type, 541-544. 

Brown-Sequard, experiments on mutila- 
tions, 367. 

Bruce, studies in mammse, 47. 

Bud variation, 181. 

Bud varieties reproduce by seeds, 181. 

Bull, E. W., originator of Concord 
grape, 134. 

Bullfinch, effect of food upon, 228. 

Bumblebee, antenna of, developed as a 
foot, 43. 

Burbank system of planting, 643. 

Burrill, experiments in crossing straw- 
berries, 184- 

Camel, development of foot of, 60. 

Castration, indirect effects of, upon the 
body functions, 100. 

Catalytic poisons, 266. 

Cats, variation in digits of, 57. 

Cattle, acclimatization of, 375 ; develop- 
ment of foot of, 58 ; meristic variation 
in digits of, 62, 63 ; reversions in, 192. 

Cave animals, 242. 

Cell, the, as a structural unit, 143, 144; 
differentiation in, 144 ; effect of grav- 
ity upon, 239. 

Cell division, as a cause of variation, 
155-181 ; irregularities in, 150-152; 
mechanism of, 145-152; outline of, 
146, 147; variation in rate of, 340; 



with and without differentiation, 149- 
150. 

Centgener plots, 644. 

Centrosome, 146. 

Cervical fistulae in mammals, 44. 

Chance, accounts for unusual occur- 
rences, 187 ; as distinct from cause, 
365 ; law of, 365, 366. 

Character, defined, 17; meaning of 
term, 11-13. 

Characters, acquired, 182; acquiredfrom 
the environment, 302-304, 308-311; 
acquired, inheritance of, 349 ; are net 
"acquired," 358-360; blended, 481; 
combine in definite proportions, 504- 
513; congenital and acquired, 354- 
356; dependent upon sex, 194-196; 
development of, how influenced, 361- 
363; dominant and latent, 13, 14; 
dominant and recessive, 514, 515; 
elementary, 14; how behave in trans- 
mission, 473-478 ; latent, 474 ; not 
necessarily adaptive, 412 ; of adult as 
influenced by development, 350; of 
the individual are those of the race, 
357; origin of, 413-415; origin and 
degeneracy of, contrasted, 415; too 
many, in animal breeding, 656, 657 ; 
variability of, in same population, 444. 

Chemical action, acclimatization to, 308- 
311 ; of secretions, 383, 384. 

Chemical effects of light, 240. 

Chemical reactions of protoplasm, 264- 
285. 

Chemicals, effect of, upon germination, 
271 ; rhythmical contraction stimu- 
lated by, 276-278. 

Chemotaxis, 271, 272. 

Chemotropism, 271, 276. 

Chromatin granules, 145. 

Chromatin matter, 145-152. 

Chromomeres, 146. 

Chromosomes, 146-152 ; but half the 
normal number of, in parthenogenetic 
individuals, 180 ; composition of, 
174; constant in number for the 
species, 146; number of, even in 
bisexual reproduction, 146 ; number 
of, reduced by maturation, restored 
by fertilization, 170; number of, 
sometimes halved, 180. 

Chrysanthemums, experiments with, by 
I)e Vries, 1 19-121. 

Cleavage, effect of outside conditions 
upon, 340 ; geometrical character of, 

339- 
Coefficient, of assortative mating, 532 ; 
of correlation, short method for 



INDEX 



717 



calculation of, 465-46S ; of heredity, 
486-488; of mode, 422, 423; of re- 
gression, 487-490 ; of variation, 433 ; 
of correlation, calculation of, 455, 
464 ; of variability, comparative, 434 ; 
of variability, meaning of, 434, 435 ; 
of variability, probable error of, 441. 

Cold, acclimatization to, 313 ; effect of, 
upon color, 264. 

Coleoptera, extra eyes in, 51. 

Color, correlation with speed in 
trotters, 468-471 ; influenced by 
temperature, 262-264 ; not due to 
presence of light, 242 ; when impor- 
tant, 31. 

Combination of characters, law of, 504- 

513- 

Combinations, formula for, 51 1 ; of two 
characters, =;o4, 505 ; of three char- 
acters, 506, 507. 

Community breeding, 674. 

Comparative value of male and female, 

587- 
Conditions of life, effect of, upon 

development, 98-105 ; influence of, 

upon parthenogenesis, 102. 
Congenital and acquired characters, 

354-356- 

Contact, effect of, upon direction of 
motion, 235 ; effect of, upon func- 
tional activity, 233-236. 

Continuity in variation, 18. 

Cope, on transmission, 354; on theory 
of growth force, 203, 204. 

Corn, acclimatization of, 375, 377, 37S ; 
correlation between length and cir- 
cumference of ears, 461 ; effect of 
selection upon, 445, 446 ; func- 
tional variation in, 83-86; influence 
of locality upon, 222 ; progression in 
oil and protein content of, 493-498 ; 
variability of, 427-431, 444, 447, 
448 ; variability of, as affected by 
fertility, 449-451 ; variation in com- 
position of, 83, 84. 

Corn Breeders' Association, system of 
planting, 646. 

Correlation, 453-471 ; coefiicients of, 
455-466; between color, sex, and 
speed, in trotters, 468-471 ; between 
length and circumference of ear, 461 ; 
meaning of, 453-455; method of 
finding coeftncient of, 460-46S. 

Correlation table, 458. 

Cows, variation in functional activity 
of, 92, 93 ; functional variation in, 
77-81 ; meristic variation in mamm2e, 
47 ; relative fertility of, 199. 



Crab, segments of, influenced by para- 
site, 100. 
Crandall, observations on curculio, 

390-393- 
Crayfish, meristic variation in oviducal 

opening, 44. 
Cross, reciprocal, 525. 
Crossing, 60S-610 ; advantages of, 608 ; 

disadvantages of, 609. 
Crystals, growth of, compared with 

growth of living matter, 143. 
Curculio, egg-laying instincts of, 390- 

393- 
Cynips, sting by, produces functional 

deviation, 98. 
Cytoplasm, 145; in development, 177. 

Dallinger, experiments in acclimatiza- 
tion to heat, 379. 

Dams, testing of, 661. 

Dandelion, influence of locality upon, 
223. 

Darbishire, experiments with mice, 524. 

Darwin, experiments in cross and self 
fertilization, 618-624. 

Davenport and Castle, experiments on 
acclimatization, 312. 

Davenport and Neal, experiments on 
acclimatization of stentor, 310. 

Death rate, Weismann on, 202. 

De Candolle, experiments on acclima- 
tization, 376. 

Degeneracy contrasted with origin, 415, 
416. 

Degeneration of useful parts, 409- 
412. 

Determinants, 152, 20S, 215. 

Determination of sex, 629-637. 

Development, 677-680 ; a study dis- 
tinct from breeding, 680 ; confusion 
of, with inheritance, 350 ; dependent 
upon external conditions, 677 ; does 
it influence transmission? 361; ef- 
fect of, upon transmission, 372, 373, 
407-409; from a half ovum, 176; 
how influenced, 361-363; influence 
of food upon, 225-230; influence of 
gravity upon, 239 ; influence of lo- 
cality upon, 221-225; influence of 
moisture upon, 230-233; influence 
of use upon, 286-288; influence of, 
upon prepotency, 574 ; limits of, 362 ; 
mechanism of, 142-154; not an 
index of inherited characters, 232 ; 
originates in geometrical cleavage of 
ovum, 339 ; requires good condi- 
tions for well-bred individuals, 678, 
679; through the cytoplasm, 177. 



7i8 



INDEX 



Deviation, average, 427 ; nature of, 
349, 350; not transmissible as such, 
349; standard, 428-431; standard, 
meaning of, 432, 433. 

Deviation and probable error illus- 
trated, 441-443. 

De Vries, experiments of, 1 14-129; ex- 
perience in plant breeding, 642 ; ex- 
periments with chrysanthemum, 119- 
121 ; experiments with primrose, 
1 21-129; production of new species 
by mutation, 1 21-129. 

Differentiation, by cell division, 149, 
150; causes of, 343; from internal 
causes, 144 ; mechanism of, 142-154; 
polarity and promorphology of ovum, 

341-343- 
Digitalis, medicinal qualities of, affected 

by locality, 223. 
Digits, meristic variation in, 53-64. 
Dimorphism of earwig, Shorthorns, 

Herefords, etc., 20. 
Disappearance of parts, 306. 
Disappearing parts, 288. 
Discontinuity in variation, 19. 
Disease, transmission of, 368, 384. 
Diseases due to absence of secretions, 

269. 
Distribution, offspring constitute a, 419. 
Dodd, William, originator of plum, 

^33- 
Dog, acclimatization of, 376 ; behavior 

of, when deprived of brain, 400, 401 ; 

meristic variation in teeth of, 50 ; 

variation in digits of, 57. 
Dogs, influence of locality upon, 224 ; 

telegony in, 186. 
Dorfmeister, experiments with butter- 
flies, 262. 
Double personality, 106. 
Doubling of parts, as head, 67-69. 
Ducks, relative weight of bones of tame 

and wild, 95. 
Dugong, variation in digits of, 57. 
Dwarfs, reasons for, 27. 
Dyads, 166. 

Earthworm, meristic variation in genera- 
tive opening of, 44. 

Earthworms, regeneration in, 317-320. 

Earwig, dimorphism of, 20. 

Eggs, regeneration in, 324, 325. 

Ehrlich, experiments with mice, 309. 

Eimer, on adaptation, 206-208 ; on the- 
ory of orthogenesis, 204-208. 

Electricity, acclimatization to, 314. 

Embryos, regeneration in, 324, 325. 

Endosperm, fertilization of, 183, 184. 



Environment, always selective, 351 ; 
bearing of, on instability of living 
matter, 290-293, 302-304 ; cause of 
evolution of the horse, 302-304 ; 
direct action of, 307; food, 225-230; 
general effect of, upon development, 
221-225 ; how influences type of race, 
290-293 ; influence of, upon cleavage, 
340 ; influence of, upon partheno- 
genesis, 178 ; influence of, upon varia- 
bility, 220-293. 

Epilepsy, transmission of, 367. 

Evidence that is not evidence, 353. 

Evolution, knowledge of, needed in 
breeding, 5; not confined to morphol- 
ogy, 76 ; Weismann's theory of, 152. 

Ewart, experiments in telegony, 1S6. 

Exercise, effect of, upon functional 
activity, 95, 96. 

Exophthalmia, transmission of, 367. 

External influences as causes of variabil- 
ity, 220-293. 

Extra wing, 43. 

Eye, effect of light upon, 243. 

Eyes, degeneration of, in cave species, 
411, 412 ; supernumerary, 51. 

Fads of the breeder, 594. 

Fan-top trees, 1 12. 

Fashion in animal breeding, 65S, 659. 

Fattening, unsuccessful in darkness, 
246. 

Fear, not present at birth, 403. 

Female, influence upon, by previous 
mating, 185-189; maturation and re- 
duction in, 165-169. 

Females, disposal of surplus, 672. 

Fere, experiments of, on chicks, 259. 

Fertility, characters correlated with, 
197 ; relative, 196-200; effect of food 
upon, 226 ; effect of, upon type, 198, 
199 ; effect of, upon type and varia- 
bility, 449-451; importance of, 199, 
584, 589 ; less with extremes of a 
race than with the means, 491 ; often 
opposed by selection, 583. 

Fertilization, by the polar body, 179, 
180; connection of, with mutation, 
180; of endosperm, 183, 184; manner 
of, 161 ; significance of, 170; influence 
of, upon sex, 632, 633. 

Fish, upstream movements, 235. 

Fisher, studies in fistulje, 45. 

Flagellata, acclimatization to high tem- 
peratures, 379, 381. 

Flammarion, experiments with light, 
245, 246. 

Flatfishes, 415. 



INDEX 



719 



Food, effect of cotton seed on pork, 228 ; 
effect of, upon bullfinches, 228 ; effect 
of, upon body temperature, 230; 
effect of, upon constitutional vigor, 
37-' 373 > effect of, upon develop- 
ment, 370-374 ; effect of, upon fer- 
tility, 226 ; effect of, upon functional 
activity, 96, 97; energy of, 229; ex- 
cess of, 227 ; how reduced by living 
beings, 228 ; influence of, upon regen- 
eration, 327, 32S; influence of, upon 
variability, 225-230; proportion of, 
used in growth, 225 ; qualitative 
effects of, 228-230 ; quantitative 
effects of, 225-227 ; well-bred races 
require more, 227. 

Foundation not in a remote female, 

595' 596. ^ 

Fraser on efficiency of cows, 78-81. 

Fraternal variability, 500-504. 

Free-martins, 176. 

Frequency distribution, typical, 421. 

Frequency distribution and the binomial 
theorem, 509. 

Frog, influence of heat upon growth of, 
258. 

Functional activity, by suggestion, 243 ; 
effects of light upon, 241-246; how 
dependent upon light, 251, 254. 

Functional variation, 75-iOQ; between 
different individuals of the same spe- 
cies, 77-91 ; due to light, 239-254 ; of 
same individual from day to day, 91- 
94; induced by castration, 100; in- 
duced by contact, 233-236; induced 
by e.xternal influences, 98, 101-105; 
influenced by food, 96, 97, 225-230; 
influenced by gravity, 236-239 ; in- 
fluenced by hard conditions, 97 ; in- 
fluenced by the reproductive faculties, 
100. 

Functions, discharged only in presence 
of light, 242, 243 ; e.xercised under 
abnormal conditions, 107-109. 

Funk, Deane N., car-load lot of prize- 
ring grade cattle belonging to, 607. 

Fiirbringer, studies in birds, 42. 

Galls, 98, 270. 

Galton, on heredity, 478; on law of 
ancestral heredity, 52S; on fraternal 
variability, 500, 501 ; on law of inherit- 
ance, 193, 194 ; on studies of stature, 
481. 

Gametic purity, 5-21. 

Gemmules, 208. 

Genetic selection, 196-200. 

Gentry, N. H., on inbreeding, 625. 



Geotaxis, 236. 

Geotropism, 236-239 ; in animals, 238 ; 
of sprout and root, 111. 

Germ, infection of, 1S5 ; influence of 
age or staleness upon, 1S2 ; individu- 
ality of, 182 ; variations in, are trans- 
mitted, 348. 

Germ plasm and transmission, 355. 

Germinal selection, 162, 213-215. 

Germinal vesicle, 166. 

Germination, effect of chemicals upon, 
271. 

Giants, reason for, 27. 

Glands, specific secretions of, 269. 

Goltz, experiments on the dog, 400, 
401. 

Gooseberry, evolution of, 130. 

Gorilla, extra incisor in, 49. 

Grading, 602-60S ; advantages of, 604 ; 
abuse of, 604 ; begin by, to get expe- 
rience, 606 ; disadvantage of, 608 ; 
disappearance of unimproved blood 
in, 602. 

Grafting, frog made up of pieces of 
two individuals, 108; illustrating 
stability of living matter, 335, 336 ; 
mammary gland into ear of guinea 
pig, 107 ; spur of cock into comb, 
107 ; two species of animal together, 
336 ; two pieces of tadpole, 336. 

Grapes, evolution of, 134. 

Gravity, effect of, upon development, 
239 ; effect of, upon living matter, 
236-239 ; effect of, upon protoplasm, 
239 ; effect of, upon regeneration, 
329-332 ; in struggle with polarity, 

237- 

Great sires, 552 ; the ten greatest, 555. 

Gross on the accessory chromosome, 
636. 

Grout, A. P., grade Angus steers be- 
longing to, 605. 

Growth, as influenced by temperature, 
254-262 ; direction of, due to light, 
249 ; direction of, influenced by heat, 
259; geometrical character of cleav- 
age in, 339 ; retarded by light, 245, 
246. 

Growth force, 203, 204. 

Guinea pig, grafting mammaij gland 
into ear of, 107 ; supposed trans- 
mission of mutilations of, 367. 

Habit not the basis of instinct, 401- 

403- 
Habits, are they transmitted ? 363, 
3S6-403 ; founded on instincts, not 
the reverse, 401-403 ; learned from 



720 



INDEX 



elders, ■^5^; not arf|nirt'd characters, 
35S-360. 

Harris, H. F., example of longevity, 89. 

Heape. experiments on rabbits, 190. 

Heart, rhythmic contraction of, 398, 399. 

Heat, acclimatization to, 311-313, 379- 
381 ; effect of, upon animal activi- 
ties, 255 ; effect of, upon direction of 
growth, 259; effect of, upon growth 
of animals, 258, 259; effect of, upon 
growth of plants, 255-257. 

Hedgehog, meristic variation in verte- 
briE of, 39. 

Heliotropism, 247 ; conditions that de- 
termine, 254 ; due to the luminous 
rays, 248 ; general principles govern- 
ing, 251, 254; of amoeba, 253, 254; 
of insects, 104. 

Hanking on the accessory chromosome, 

635- 

Herbst, experiments in regeneration, 
328. 

Herd, management of, during depres- 
sion in prices, 665-666; records of, 
666-670 ; unity of, 662 ; without a 
head, 664. 

Heredity, 473-547 ; coefficient of, 4S6, 
488 ; coefficients of different rela- 
tionships, 488 ; famous grandsires, 
556 ; law of ancestral, 525-534 ; man- 
ner of, 420-431 ; material basis of, 
209; mathematical nature of, 510; 
mean of offspring not mean of the 
parents, 490 ; measure of, 486 ; mis- 
conceptions of, 473 ; offspring differ 
from parents, 482, 483 ; offspring 
more mediocre than the parents, 
484-486 ; origin of the exceptional 
individual, 499, 500 ; progression in, 
492-498; proper conceptions of, 473 ; 
statistical methods in study of, 426, 
478 ; what is transmitted? 511. 

Herefords, dimorphism in, 20. 

Hero, the inbred morning-glory, 622. 

Herringham, studies on nerves, 43. 

Homoeosis, 37 ; in insects, 43 ; in verte- 
bra and ribs, 40-42. 

Honeybee, eyes united, 65. 

Hopkins, experiments in corn breeding, 
83-86, 493-498- 

Horns, meristic variation in, 52, 53, 66 ; 
regeneration of, 326. 

Horse, begging instinct in, 353 ; causes 
of evolution of, 302-304; defective 
voice in, 353 ; development of foot 
of, 58, 59; evolution of, 298-30^; 
extreme age of, 89; meristic varia- 
tion in digits of, 60, 61. 



Horses, acclimatization of, 375; corre- 
lation between color, sex, and speed, 
4O8-471; inbreeding in, 624; power 
of transmission among, 408 ; telegony 
in, 185. 

Horseshoe kidney, 65. 

Hot springs. Infusoria in, 311; life in, 

379- 

Houghton, Abel, originator of goose- 
berry, 130. 

Hunter, experiments in grafting, 107. 

Huntington, Randolph, on breeding, 
624. 

Hybrids, character of descendants of, 
514-521; Mendel's law of, 513-525; 
sterility of, 607. 

Hypertrophy, 2S8, 289. 

Idants, 173. 

Ideals in selection, 578, 579. 

Idioplasm, 152, 208. 

Ids, 146, 208. 

Illinois station, system of planting at, 646. 

Immunity, natural and acquired, 382. 

Improvement, upper limits of, 582. 

Inbreeding, 613-626; advantages of, 
614, 615; A. J. Lovejoy on, 625; 
among animals, 624-626 ; Dai"win's 
experiments on, 618-624 ; disadvan- 
tages of, 615; forms of, 613, 614; 
how to practice, 626; often more 
vigorous than outbreeding, 622-624 ; 
lack of vigor and low fertility com- 
mon defects, 6i6, 617 ; N. H. Gentry 
on, 625 ; not all inbred individuals 
inferior, 620-623 ; not necessarily dis- 
astrous, 616-626; Randolph Hunt- 
ington on, 624 ; special dangers in, 
616; total effects of, 619, 620. 

Individual, the, 352 ; possesses all the 
characters of the race, 357, 360. 

Individuality in offspring from same 
parents, 503. 

Infertility a common defect, 616, 617; 
effect of, 584, 589. 

Inheritance, complex, 527; belated, 
475; blended and exclusive, 475; 
from separate ancestors, 527 ; from 
the race, 193, 1 94 ; not limited to sex, 
474 ; of acquired characters, 292, 349; 
offspring more mediocre than the 
parents, 484-486; particulate, 476; 
progression in, 492-498. 

Inoculation, immunity by, 382. 

Insect poisons, 270. 

Instability, of living matter, illustrated 
by origin of differentiated tissue, 336- 
338 ; of protoplasm, 398. 



INDEX 



721 



Instinct, 104-106; is it founded on 
habit ? 388-390 ; not founded on 
habit, 401-403; not unerring, 389. 

Instinctive acts, a series of reflexes, 
398-401 ; not uniformly performed, 
390-394. 

Instincts, are they inherited habits ? 
386-403; due to external stimuli, 
252 ; intelligence not necessary to, 
397, 398; nature of, 387, 388; origi- 
nate in reflex action, 394-397 ; not 
always adaptive, 394. 

Intelligence not necessary to compli- 
cated acts, 397, 398. 

Internal influences affecting the race, 
196-217. 

Intra-uterine influences, 189-191. 

Jochemke, variation in functional 
activity of, 92, 93. 

Kangaroo, development of foot of, 60. 
Kanthack, experiments with snake 

poison, 309. 
Kerrick, L. H., car-load lot of graded 

steers, 603 ; on herd records, 668, 

669. 

Lamarckians, opposers of, 413; views 
of, 413. 

Lancaster, Ray, defines thremmatol- 
ogy, I. 

Latent characters, 474. 

Law of ancestral heredity, 194, 525-534. 

Law of chance, 365, 366. 

Life, material basis of, 213. 

Light, acclimatization to, 313 ; chemical 
effects of, 240 ; effects of, upon fixa- 
tion of carbon, 239 ; effect of, upon 
functional activity, 241-246; effect 
of, upon living matter, 239-254 ; effect 
of, upon regeneration, 328 ; general 
effects of, 251, 254; influence of, 
upon direction of growth, 247 ; influ- 
ence of, upon eyes of dead sharks, 
395 ; influence of, upon locomotion, 
247 ; not necessary to development 
of color, 242 ; not necessary to devel- 
opment of vigor, 244 ; specific rays 
of, that exert effect upon growth, 245, 
246; vital limits as to, 244. 

Line breeding, 610-613 ; advantages of, 
61 1 ; best system for improvement of, 
612; disadvantages of, 611, 612. 

Living matter, distinguished from non- 
living, 142-143; influence of light 
upon, 239-254; parallelism with 
non-living matter, 210, 211; relative 



stability and instability of, 295-346 ; 
response to gravity, 236-239. 

Locality a comprehensive term, 224. 

Locomotion, direction of, due to light, 
250. 

Loeb, experiments in chemotropism, 
273-276; experiments in heliotro- 
pism, 250-254 ; experiments in par- 
thenogenesis, 278-282 ; experiments 
in rhythmic contraction, 276-27S; 
observations upon Infusoria, 308. 

Longevity, 201, 202; earher offspring 
live longest, 502. 

Lothelier, moisture experiments, 231. 

Lovejoy, A. J., line-bred swine belong- 
ing to, 611, 612; on herd records, 
670 ; on inbreeding, 625. 

Lubbock, experiments with ants, 273. 

McClung on the accessory chromosome, 

635- 
Male, maturation and reduction in, 169, 

170. 
Male and female, comparative value of, 

587. 

Mammas, meristic variation in, 46, 47. 

Mammary tissue, grafted on ear of 
guinea pig, 107 ; in various parts of 
the body, 46. 

Man, auricular appendages on, 45 ; 
cervical fistulae in meristic variation 
in digits of, 54, 55, 69; meristic vari- 
ation in mammae of, 47 ; meristic 
variation in ribs of, 40, 4 1 ; milk se- 
cretion not confined to females, 107 ; 
telegony in, 188. 

Manatee, variation in digits of, 54. 

Marks due to prenatal influences, 189- 
191. 

Material basis of life, 213. 

Maturation in the female, 165-169. 

Maturation and reduction, a cause of 
variation, 1 63-1 81 ; in animals and 
plants compared, 165; in male and 
female compared, 164. 

Mean, calculation of. 424; of offspring 
not the mean of the parentage, 490 ; 
practical use of, 425 ; probable error 
of, 440. 

Measurements, hints on taking of, 435 ; 
scheme of, 436. 

Meat production, variation in, 81-82. 

Mechanism of development and differ- 
entiation, 142-154. 

Melon, influence of locality upon, 221. 

Men, milk secretion by, 107. 

Mendel, Gregor Johann, 513. 

Mendel's experiments, 516-521. 



722 



INDEX 



Mendel's law, 513-525; experimental 
evidence on, 516-521 ; experiments 
with mice, 524. 

Mendel's law and gametic parity, 521. 

Merinos in New Zealand, 223. 

Merism, ^^. 

Meristic variation, 33-74 ; cervical fis- 
tulae and auricular appendages, 44- 
46; doubling of complicated parts, 
64-69; due to cell division, 72, 158; 
homoeosis in, 37 ; in digits, 53-64 ; 
in eyes, 51; in generative parts, 44; 
in head, 67, 68; in horns, 52, 53; in 
legs, 64 ; in mammas, 46, 47 ; in radial 
series, 70-73 ; in spinal nerves, 42 ; 
in teeth, 48-51 ; in vertebrae and ribs, 
39-42 ; in wings, 51. 

Mice, acclimatization of, to ricin, 309 ; 
variation in digits of, 58. 

Microsomes, 146. 

Mid-parent, Gallon's, 481. 

Mid-parent deviation, formula for, 531. 

Mid-parent variability, formula for, 531. 

Milk production, variation in, 78-80, 
92, 93 ; transmitted by males, 360. 

Milk secretion by males, 105, 107. 

Minnesota station, system of planting 
at, 644. 

Mitosis, as a cause of variation, 155- 
181; details of, 145-152; irregular- 
ities in, 150-152; pathological, 150- 

Mixed breeding, purity m, 507. 
Modal coefficient, 422, 423. 
Mode, the, 421, 422; empirical and 
theoretical, 422 ; practical value of, 

423- 
Modifications due to external influences, 

transmission of, 348-4 r 7. 
Moisture, effect of, upon development, 

230-233 ; effect of, upon spiny 

growth, 231. 
Monte Carlo and roulette, 365. 
Morgan, observations on acclimatiza- 
tion to heat, 311; on fear in chicks, 

403. 
Morgan horse, 296. 
Morning-glory, Darwin's experiments 

in inbreeding, 621-624. 
Morphological variation, 25-29 ; causes 

of, 27 ; in mulberry leaves, 26. 
Moss roses, a bud variety, iSi. 
Moths, flight of, determined by light, 

250. 
Movement induced by contact, 234. 
Mulberry leaves, polymorphism in, 26. 
Multiplying plots, 650. 
Multipolar mitosis, 151. 



Mumford, experiments in feediiig, 82 ; 
on pork production, 228. 

Muscle fiber, effect of light upon, 247. 

Mutability of species, 298-305. 

Mutants, 21 ; origin of, in toadflax, 
1 1 5-1 18. 

M utation, biological significance of, 1 36, 
137; distinguished from ordinary va- 
riation, no; economic significance 
of, 135-136; in chrysanthemum, 119- 
121; in primrose, 1 21-129; l^ws of, 
127-129; in toadflax, i 15-1 18; in 
American native plants, 129-135; in 
general, 110-138; relation of, to re- 
duction and fertilization, 180. 

Mutation and elementary species, 128. 

Mutation and parthenogenesis, 179. 

Mutilations, are they transmitted ? 363- 
368 ; experiments upon transmission 
of, 367 ; resemblance of, to natural 
deformity, 366. 

Nageli, experiments with copper, 268. 
Narwhal, meristic variation in tusk of, 

70. 
Natural selection always at work, 588. 
Nectarine, mutant of the peach, 112. 
Neo- Darwinians, 354. 
Neo-Lamarckians, 354. 
Nerves, meristic variation in, 42. 
Neugebauer, studies in mammje, 47. 
Nucleus, 145-152. 

Odors, attraction of, 275. 

Oil content of com, 83-85 ; effect of 
selection upon, 445, 446 ; progression 
in breeding for, 496-498. 

Old Granny, example of longevity and 
extreme fertility, 89, 90. 

Oocyte, 165. 

Oogonia, 165. 

Orientation, 247. 

Origin of characters, 413-415. 

Orthogenesis, 204-208 ; explained by 
germinal selection, 215. 

Osborn, researches on evolution of the 
horse, 302. 

Ossification, 99. 

Otocyon, teeth of, 50. 

Overfeeding, evil effects of, 227. 

Ovum, 161, 165; polarity of, 341-343; 
promorphology of, 341 ; segmenta- 
tion of, without fertilization, 177- 
180. 

Oxygen, effect of, upon protoplasm, 265. 

Panmixia, 288. 

Parry, originator of blackberry, 132. 



INDEX 



723 



Parthenogenesis, 162; but one polar 
body in, 179; influenced by condi- 
tions of life, 178; influenced by tem- 
perature, 28 1 J Loeb's experiments in, 
278-2S2 ; but half the normal num- 
ber of chromosomes in, 180. 

Parthenogenesis and mutation, 179. 

Parthenogenetic reproduction, variation 
in, 177-180. 

Particulate inheritance, 476. 

Paulmier on the accessory chromosome, 

635- 

Pearson, on the bathmic influences, 
203 ; on causes of variability, 220 ; on 
fertility, 196-198 ; on law of ancestral 
heredity, 529 ; on reduction of varia- 
bility, 536; on telegony, 188. 

Pedigree, importance of, 592 ; records 
of, 670-672. 

Pedigrees, fashionable, 595. 

Peloric flowers in toadflax, 11 5-1 18. 

Performance, as a guide to breeding 
powers, 558-567 ; records in plant 
breeding, 650. 

Pfeffer, experiments on chemotropism, 

273- 

Photosynthesis, 240. 

Phototaxis, 248. 

Phototonus, 248. 

Physiological selection, 201, 589. 

Physiological units, 14, 17, 152, 208- 
213; as affected by reduction, 170. 

Pigs, acclimatization of, 375; develop- 
ment of, 58 ; meristic variation in 
digits of, 63. 

Planarian, regeneration of, 321, 322, 
334, 335 ; regeneration of starving, 
327 ; regeneration of, when split, 335. 

Plant breeding, 639-65 1 ; advantages 
and limitations of, 639-641 ; plot sys- 
tem for, 644-646 ; soil and culture 
conditions for, 641-643; systems of 
planting in, 643-649. 

Plant lice, effect of conditions upon 
reproduction, 102; parthenogenetic 
only at high temperatures, 28 1. 

Plants, effect of heat upon growth of, 
255-257 ; regeneration in, 325. 

Plot system of planting in breeding 
work, 644-646. 

Plums, evolution of, 133. 

Poison ivy, immunity to, 308. 

Poisons, acclimatization to, 30S-311; 
catalytic, 266, 267 ; from insects, 270 ; 
toxic, 268. 

Polar bodies, 164; formation of, 167 ; for- 
mation of, illustrated, 1 68 ; fertilization 
by, 179, 180; formation of second, 167. 



Polarity, in struggle with gravity, 237 ; 
of ovum, 341-343- 

Pollination, indirect effect of, 185. 

Polymorphism in practical breeding, 
476, 477 ; with regard to sex, 20. 

Poplar, acclimatization of, 376. 

Population, 421 ; type of, 422. 

Pork, effect of cotton seed upon, 228. 

Precipitin test, 382. 

Preferential mating, 163. 

Prenatal influences, 189-191. 

Prepotency, 551, 575; as affected by 
age, 573 ; as indicated by perform- 
ance, 558-567 ; as related to consti- 
tutional vigor, 573 ; as shown by 
trotting records, 551-566; influence 
of development upon, 574 ; because 
of sex, 567-570. 

Primrose, seven mutants in eight gen- 
erations of, 127. 

Probable error, of coeflicient of varia- 
bility, 441; of mean, 440; of stand- 
ard deviation, 440 ; meaning of, 
437-440- 

Probable error and deviation illustrated, 

441-443- 

Progression, a few offspring extreme, 
492-498 ; in oil content, 496-49S ; in 
protein content, 493-495 ; origin of 
the exceptional individual, 499, 500. 

Proof by method of instance, 187, 366. 

Protein content of corn, effect of selec- 
tion upon, 445, 446; progression in 
breeding for, 494, 495. 

Protoplasm, a chemical substance with 
chemical properties, 144; activity of, 
due to external as well as to inter- 
nal impulses, 398-401 ; as influenced 
by chemical agents, 264-285 ; effect 
of contact upon, 233-236; effect of 
gravity upon, 239 ; effect of heat and 
cold upon, 255; irritation of, 398; 
effect of external agents upon, 396, 
397; physical basis of life, 142, 143; 
relative stability and mutability of, 

295. 346. . . 

Protozoa, but one maturation division 

in, 165. 
Purity of blood lines essential, 579. 
Python, meristic variation in vertebrae 

and ribs of, 39, 40. 

Qualitative effects of food, 228-230. 
Quantitative effects of food, 225-228. 

Race, affected by internal influences, 

iq6-2i7; extinction of, 415. 
Radial symmetry, ^4, 



724 



INDEX 



Random sample, 420. 

Rat, tail of, grafted into back, 107. 

Rational selection, 592, 593. 

Rats, variation in digits of, 5S. 

Reaumur, experiments in regeneration, 
316. 

Reciprocal cross, 525, 610. 

Records, in animal breeding, 666-672 ; 
in plant breeding, 645-649 ; of the 
herd, 666-670; of pedigree, 670-672. 

Redtield, Casper L., on prepotency, 574 ; 
on transmission, 407, 408. 

Reduction, a cause of variability, 163- 
181, 175, 176; apparent purpose of, 
167; connection with mutation, 180; 
end products of, 167, 16S; how ac- 
complished, 169 ; illustrated, 168; in 
the male, 169, 170; in the female, 
165-169; in male and female com- 
pared, 164; in plants, 1 71-173; in 
animals and plants compared, 165; 
losses sustained by, 170; opportuni- 
ties for accident during, 171 ; Weis- 
mann's prediction concerning, 173, 
174; results in loss of chromatin 
matter, 170, 173; significance of, 170. 

Reflex action the basis of instinctive 
acts, 394-397- 

Regeneration, bearing of, on stability 
of living matter, 316-332; by trans- 
formation, 232 ; character of restored 
part in, 326, 327 ; effect of age upon, 
331 ; effect of flowering period upon, 
331; elTect of food upon, 327, 328; 
effect of gravity upon, 329-332 ; 
effect of light upon, 328 ; effect of 
temperature upon, 327 ; first in form, 
afterward in size, 317; growth in, 
not uniform, 317, 318; from oblique 
surface, 334 ; heteromorphosis in, 
332; internal factors in, 332-335; in 
animals, 316; in earthworms, 317- 
320; in embryos and eggs, 324, 325; 
in fish, 318; in higher animals, 325, 
326; in the planarian, 321, 322, 334, 
335 ; in plants, 2-^ ! i'l salamander, 
316; in actinian, 334; lateral, 333, 
335; not always complete, 318-320, 
323, 325; polarity in, 320, 329-333; 
what determines character of re- 
stored part, 333. 

Regression, advantage and disadvan- 
tage of, 485 ; as to stature, 479-481 ; 
diagram of, 4S9 ; offspring more me- 
diocre than parents, 484-486. 

Regression coefficient, 466, 487-490. 

Regression table, 479-482. 

Reversion, 16, 192-194. 



Reversion and atavism, 305. 

Rheotaxis, 235. 

Rhinoceros, development of foot of, 60. 

Ribbert, grafting mammary gland on ear 
of guinea pig, 336. 

Roebuck, meristic variation in horns 
of, 53' 65, 66. 

Romanes, on instinct, 389; on trans- 
mission, 354 ; on transmission of 
mutilations, 367. 

Roots, development of, by external 
conditions, 104; growth of, in run- 
ning water, 235. 

Rose, record of, with Nora, 78-80. 

Roulette wheel, how made up, 365. 

Roux, experiments upon segmenting 
frogs' eggs, 343 ; on preparation of 
antitoxin, 310. 

Row system of planting in breeding 
work, 646-649. 

Sachs, experiments on growth of plants, 
256. 

Salamander, regeneration in, 316. 

Saline solutions, effect of, upon devel- 
opment, 2S2-2S5. 

Sample, random, 420. 

Sawfly, antenna of, developed into a 
foot, 43. 

Schmankewitsch, experiments with Ar- 
temia, 102, 283. 

Sea urchin, Loeb's experiments with, 
278, 282. 

Seal, variation in digits of, 57. 

Secretions, chemical action of, 383, 384. 

Seed production a business, 650. 

Seedlings, response of, to gravity, 236. 

Seeds, effect of moisture upon, 232. 

Segmentation, dependence of, upon 
water content, 178; geometrical 
character of cleavage in, 339 ; not 
dependent on fertilization, 178. 

Selection, 577-598 ; blemishes and 
accidental injuries bearing on, 590; 
cessation of, 288 ; effect of, upon type 
and variability, 445, 446; general 
principles involved in, 581-592 ; his- 
torical knowledge of the breed essen- 
tial in, 579, 581 ; ideals in, 578, 579; 
importance of pedigree in, 592 ; in- 
creased number of " points " in, 590 ; 
indirect effects of, 447-44S ; influence 
of age in, 589; fallacy of "foundation" 
females in, 595, 596 ; limit of power 
of, to reduce variability, 534, 537 ; 
natural selection always at work, 
588 ; need of large numbers for, 584 ; 
need of the actual test for, 586; 



INDEX 



725 



objects of, 579; often against vigor 
and fertility, 583 ; pliysiological, 589 ; 
power of, to modify type, 291, 537- 
544; progressive, 197; purpose of, 
581; rational, 592, 593; reduces to 
utility basis, 591 ; results in absolute 
increase of quality, 582 ; reversal of, 
288; size in dam, quality in sire, 5S8 ; 
the exceptional breeder not always 
the exceptional individual, 585 ; upper 
limits of improvement, 583 ; value of 
the exceptional breeder, 5S5; visible 
characters deceptive in, 508, 510. 

Selective death rate, 201, 202. 

Selective influence of environment, 35 1 . 

Sewall, experiments with snake poison, 

309- 
Sex, correlation with speed in trotters, 
468-470 ; determination of, 629-637 ; 
differences slight, 630 ; in mammals, 
634 ; in bees, 632 ; in plant lice, 632 ; 
in wasps, 633 ; influence of, upon 
development of characters, 194-196; 
influence of fertilization upon, 632, 
633; influence of nutrition upon, 631; 
inheritance not limited to, 474 ; re- 
lated to the accessory chromosome, 

634-637- 
Sex determination, theories upon, 629, 

630. 
Sexes, comparative variability of, 570, 

573 ; equipotent, 568. 
Sharks, effect of light on eyes of dead, 

395- 

Sheep, development of foot of, 58 ; me- 
ristic variation in digits of, 63. 

Shorthorns, polymorphism in, 20. 

Show-ring consequences, 660. 

Shy breeders, 119, 200. 

Sire, quality in, 58S. 

Sire more than half the herd, 5S7. 

Sires, great, 552; market for, 673; of 
sires and sires of dams contrasted, 
553-555 ; testing of, 662-664. 

Smith, Kittie, writing with feet, 286, 
287. 

Snakes, rudimentary legs of, 58. 

Spallanzani, experiments in regenera- 
tion, 316. 

Species, supposed conversion of, 283. 

Sperm cell, 161. 

Spermatocytes, 169. 

Spermatozoon, 161 ; function of, 28 1. 

Spinal nerves, meristic variation in, 42. 

Spireme, 146. 

Sports, 21, III. 

Stability, of type, 296, 297 ; shown 
by reversion, 305 ; of living matter 



illustrated by grafting, 335, 336 ; by 
regeneration, 316-335. 

Stabihty and instability of living matter, 
295-346 ; illustrated by development 
and differentiation, 23<i- 

Standard deviation, 42S-431 ; con- 
trasted with average deviation, 431 ; 
illustrated, 441-443; meaning of, 
43-' 433 ' piobable error of, 440 ; 
shortened method of, 429. 

Standards should not be changed, 

579- . 
Starvation, effects of, upon regenera- 
_ tion, 327. 
Statistical methods, 426 ; need of, in 

heredity studies, 47S. 
Stature, transmission of, 480-484, 488- 

493' 499- 

Steers, functional variation in, 82. 

Stentor, acclimatization of, to HgCl, 
310; regeneration in, 323. 

Stereotropism, 250. 

Sterility of hybrids, 609. 

Sterling, originator of blackberry, 133. 

Stiip, 14, 152, 208. 

Strasburger, growth below zero, 313. 

Strawberry, evolution of, 131. 

Struthers, observations on ribs, 40. 

Stunted animals, 225. 

Substantive variation, 30-32 ; impor- 
tance of, 31. 

Suprarenal glands, 3S3. 

Swine, development of foot of, 58 ; 
inbreeding in, 625. 

Symmetry, 34-37 ; bilateral, 34, 65-68 ; 
dorsal and ventral, as distinct from 
right and left, in variable parts, 68- 
70 ; longitudinal, 36 ; radial, 34. 

Syndactylism, 63, 66. 

Systems of breeding, 599-627. 

Tapir, development of foot of, 60. 

Teeth, meristic variation in, 48-51. 

Telegony, 185-1S9; in dogs, 1S6 ; in 
horses, 185; in man, 188; proof by 
method of instance, 187 ; scientific 
objections to, 188. 

Teleology, principle not universal, 207. 

Temperature, acclimatization to, 311- 
313, 376-3S1 ; all-pervading, 264 ; ef- 
fect of, upon color, 262-264 ; effect 
of, upon growth, 254-262; effect of, 
upon parthenogenesis, 281 ; effect of, 
upon regeneration, 327. 

Temperature of the body, 230. 

Ten great sires, 555. 

Teratology, 100. 

Testing sires and clams, 660-664. 



726 



INDEX 



Testing young females, 661. 

Tetrads, 166. 

Thigmotaxis, 235. 

Thremmatology, compared -with evolu- 
tion, 2 ; defined, i ; more than a study 
in morphology, 8 ; problems of, out- 
lined, 3-5. 

Thyroid, effect of extirpation of, 383. 

Toadflax, experiments with, by De Vries, 
115-118. 

Toxic poisons, 268. 

Transmission, 347-417 ; heterogeneous, 
426; how characters behave in, 473- 
478; manner of, 420-431; effect of 
acclimatization upon, 374-380; effect 
of development upon, 407-409 ; of 
disease, 368, 384 ; of effects of food, 
370-374 ; of effects of use and dis- 
use, 404-407 ; of habits, 386-403 ; of 
immunity, 382; of mutilations, 364- 
368 ; of stature, 480 ; of variation, 
348-417 ; not unless germ is affected, 
416, 417; offspring not like parents, 
482, 483 ; offspring more mediocre 
than the parents, 484-486 ; origin of 
the exceptional individual, 499, 500 ; 
progression in, 492-498 ; what is 
transmitted, 511. 

Trembley, experiments on regeneration, 
316. 

Trotters, correlation between color, 
sex, and speed, 468-471. 

Trotting records showing prepotency, 
551-566. 

Tumors, 99, 271. 

Turtle, double head of, 67. 

Twins, 176; identical, 176; from a sin- 
gle ovum, 176. 

Type, as distinct from the individual, 
352; conceptions of, 420-425 ; effect 
of environment upon, 290-293 ; ef- 
fect of fertility upon, 198, 199, 449, 
451 ; effect of selection upon, 445, 
446 ; mutability of, 298-305 ; natural, 
422 ; power of selection to modify, 
537-544; selection standard for, 420, 
425; stability of, 296, 297, 541, 544. 

Type and variability, 419-451. 

Use a function of structure, 387. 

Use and disuse, effect of, 285-290 ; ef- 
fect of, upon functional activity, 95, 
96; effects of, when transmitted, 404- 
407 ; influence on transmission, 363. 

Variability, among offspring of same 
parents, 500-504; as affected by 



fertility, 449-451 ; coefficient of, 433; 
determined from groups, 426 ; devi- 
ation from type, 425; effect of selec- 
tion upon, 445, 446; erroneous con- 
ceptions of, 425, 426; highest in 
fertile soils, 642 ; in heights of broth- 
ers, 501 ; in oil and protein, 445, 446 ; 
in physical characters of corn, 447, 
44S ; limitations of, 8, 9 ; limit to the 
reduction of, 534-537 ; measure of, 
by average deviation, 427 ; measure 
of, by standard deviation, 428-431 ; 
nature of, 10, 11 ; of different char- 
acters in same population, 444 ; of 
sexes, 570-573; ultimate unit of, 
15-17; units of, 208-213. 
Variation, bud, 181 ; causes of, T41- 
347 ; caused by bisexual reproduc- 
tion, 160-163 ; caused by cell division, 
1 55-1 81 ; caused by external influ- 
ences, 220-293; caused by reduc- 
tion process, 163-181, 175, 176; 
causes of, must be studied, 141 ; con- 
fined to racial characters, 358 ; con- 
tinuous and discontinuous, 18-22; 
correlated, 16; does not extend to 
non-living matter, 23 ; due to age or 
staleness of germ, 182; due to tem- 
perature, 262-264; functional, 75- 
109 ; functional, due to age, 94 ; func- 
tional, between different individuals 
of the same species, 77-91 ; func- 
tional, due to use or disuse, 95, 96 ; 
functional, from day to day, same in- 
dividual, 91-94 ; functional, induced 
by external influences, 98, 101-105; 
functional, influenced by feed, 96, 97 ; 
how far possible, 295-346 ; induced 
by food, 225-230; influence of mois- 
ture upon, 230-233; influenced by 
fertility, 196-200; influenced by the 
reproductive functions, 100; influ- 
enced by slight chemical changes, 
210, 211 ; in chemical composition of 
seeds, — corn, 83-86 ; in fertility, 90 ; 
in general body faculties, 86 ; in meat 
production, 81-83; i" milk secretion, 
77-8r, 91-93; in parthenogenetic re- 
production, 177-180; in sugar pro- 
duction, 86 ; in race, caused by ex- 
ternal influences, 290-293 ; in rate of 
cell division, 340; in vital functions, 
87-89; internal causes of, 155-217; 
kinds of, 17-23; morphological, sub- 
stantive, meristic, functional, 22 ; 
meristic, 33-74 ; morphological, 25- 
29; substantive, 30-32; quantitative 



INDEX 



727 



and qualitative, 17; nature of, 356- 
364 ; nqt notably less in partheno- 
genesis, 178; through inheritance of 
modifications, 292 ; units of, 208-2 1 3 ; 
universality of, 7, 8. 

Variations, due to causes internal to the 
germ, are transmitted, 348; due to 
external influences, transmission of, 
348-417 ; due to causes not affecting 
the germ not transmitted, 41G, 417; 
occur according to the binomial the- 
orem, 508, 509. 

Varieties, duration of, 544, 545. 

Vigor, often opposed by selection, 583. 

Vital limits as to light, 244. 

Vochting's experiments on gravity and 
polarity, 237. 

Wallace on the accessory chromosome, 
636. 

Water, effect of, upon growth, 230-233. 

Wattles, 46. 

Wayland, originator of plum, 133. 

Weeping varieties, 112. 

Weismann, experiments with butter- 
flies, 262-264 ; o" death point, 202 ; 
on germinal selection, 214 ; on origin 
of characters, 413, 414 ; prediction of. 



173, 174; prediction concerning loss 
of hereditary matter, 173, 174; on 
transmission, 354. 

Whale, variation in digits of, 57. 

Wheat, acclimatization of, 376; influ- 
ence of locality upon, 222. 

White, Hugh, originator of Clinton 
grape, 134. 

Whitney, fund for exploration, 302. 

Willow, effect of gravity on growth of, 

Wilson, John, originator of blackberry, 

132. 
Wilson on the chromosome, 634. 
Wing, supernumerary, 43. 
Wings, supernumerary, 51. 
Writing with the feet, 286, 2S7. 

Xenia, 183, 184. 

Young breeders, 675. 

Yucca moth, 105; instinctive acts of, 

38S. 
\ ule's formula, 456, 457. 

Zoja, experiments in regeneration of 
blastomeres, 325. 



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